Constitution is everyone’s second-most-important ability
That’s it, that’s all it comes down to. There are elf subraces without a Constitution penalty; those are fine. But for “Elf” race, and most elven subraces, you get −2 Constitution, and that’s just terrible. Even if Dexterity is your most-coveted ability score, you can get +2 Dexterity without taking a −2 penalty to Constitution, and since that is an option, you will want to do so because even if Dexterity is more important, Constitution still is important.
And it is really important. A +2 to Dexterity means you get +1 to some rolls. They can be some important rolls, initiative, attack, stealth, maybe damage if you work at it. But it’s still just +1.
But Constitution, unlike most other ability scores, has a multiplicative effect (Intelligence does too, with skill points, but that only matters to some characters; HP matters to everyone). You don’t lose 1 life with a −2 to Constitution, you lose 1 life per level. And that winds up being a pretty big chunk of life.
Also, and this is admittedly very much secondary, Fortitude saves tend to be (much) more important than Reflex saves. Reflex saves tend to halve some HP damage, and direct-damage, particularly magical direct-damage, as in the sort of thing you can halve with a Reflex save, tend to be kind of mediocre. Fortitude saves often ward off very unpleasant things, like ability damage (disease, poison) or straight-up death. All else being equal, Fortitude tends to be the more important saving throw. Will tends to be even more important (because a failed Will save also often involves death or ability score damage, or worse can mean possession or mind-control).
The rest of the elf racial features are just... minor
The rest of the elf racial features are nice, but niche or minor. They just do not measure up to the sheer loss that the −2 Constitution represents.
The trance thing rather than sleeping is cool, but ultimately it doesn’t represent a dramatic advantage; rotating guards are still a really good idea, as are alarm spells and the like. Outside of very-low levels, sleep is not a major danger. Note that trancing does not reduce the amount of sleep that arcane spellcasters need. If it did, that would be a really big deal (possibly too good but really, I doubt it), but it doesn’t.
Automatic searching is cool, except if it’s really important you’re probably already searching for it (so the racial ability often just winds up being a minor thing the DM threw in to give the elf player a bone).
In most games, it’s the kind of thing that, if no one was playing an elf, somehow just magically wouldn’t have been an issue in the first place. DM-time is a valuable thing to be spent wisely, which means it’s usually a bad thing for a DM to give much thought to a room the PCs are never going to find. If the players need to find the room and don’t have an elf, the DM is going to find some other way to hint at it, or just move it somewhere that they’ll find it. DMs often do similar things for parties that lack trapfinders or trackers. The lack of these things may, in theory, reduce the party’s effectiveness at a particular task, but the more important the thing to be found is, the more likely the DM is to make sure the party finds it.
In really sandboxy games, the DM might give some thought to random rooms, trying to imagine where those rooms would logically be from the perspective of the building’s designers. Or, if you are playing a pre-made module, it’s entirely possible that the authors of the module threw in random hidden rooms just because someone might be playing an elf.
In other words, this feature can, and possibly will, occasionally get you a nice little thing. It might provide a short-cut, an extra bit of treasure, whatever. Those are nice things. However, even when there is something to find with auto-search, the room still cannot be crucial if it’s unlikely to be found by parties without elves (or the party elf just doesn’t have a lot of ranks in Search or just flubs the Search check). Because if the room is crucial and the party is unlikely to find it, there’s a high risk of the game suddenly grinding to a halt while party has no idea what it is they need to progress. And no matter how you slice it, that’s pretty bad for the game. So this feature will just about never make-or-break the campaign, or a character’s success, unless the DM very artificially forced something in just to make the feature important (see This Looks Like a Job for Aquaman).
Weapon proficiencies are cheap and easy to come by for almost everyone who cares. After all, players don’t play commoners. If you actively use weapons as an adventurer, you almost-definitely already have proficiency in the weapons you want to use. Very few classes swing weapons regularly, yet don’t have proficiency in the weapons elves are automatically proficient in. And even when that does happen, they usually have something almost as good (a Simple variant of the same weapon, for example; the difference is a minor +1 to damage, on average, for having the Martial version).
The one sort-of major exception, wizards who cannot cast spells, still isn’t really a great example, for a couple of reasons.
First, between all the methods wizards have to maintain their spell slots, the quantity of spell slots they have available, and their own ability to decide whether or not to put themselves at risk of needing spell slots they don’t have, most cases of this are fairly contrived.
Second, a wizard spending any significant amount of time where he has nothing better to do than shoot a bow he’s crap at shooting is an indication that there is something seriously wrong with your campaign. In essence, a player who has chosen to play a wizard did so in order to cast spells, not to be a piss-poor archer. He is not good at shooting a bow, be it a crossbow or a longbow, and it’s not what he’s here to do. Which means that, if you as a DM are doing your job right, it should be very rare that the wizard is reduced to plinking things with a bow. The wizard should have better things to do be doing the overwhelming majority of the time, because otherwise you’re being fairly rude to the player in question, invalidating his choices and wasting the time he put into building the spellcasting abilities of the character. Having “better things to do” might not be casting spells; throwing characters outside their forté can be interesting if done right. But having the player sit there going “well, I guess I’ll take another pot-shot with my bow; can’t really do anything else,” means you, as a DM, are failing that player for as long as that goes on. If it’s brief, fine: not everyone needs to have the spotlight at all times; that’s impossible. But if this is going on a lot in your campaign, you are doing something very wrong.
Finally, if I as a wizard really care about this, I can always just be Human and take Martial Weapon Proficiency as my bonus feat, or swap Scribe Scroll for it using the Unearthed Arcana variant, or whatever. I don’t get the +2 Dex, but I avoid the −2 Con, which is going to matter to me more and more often. Even if I’m worried about being reduced to plinking away with a bow, I don’t need four proficiencies, just one. I definitely don’t want to get into melee with a d4 HD, a −2 Con, and a rapier, that’s for damn sure.
So, ultimately, those racial features, while kind of nice, just aren’t worth it for −2 Constitution.
There are exceptions, of course, particularly for elf subraces.
Several elf subraces have bonuses to Intelligence, which are otherwise very difficult to come by (though the same argument about Dexterity applies to Intelligence, with a limited set of books you might not be able to get +2 Intelligence without taking −2 Constitution).
There are a select few feats and prestige classes that require proficiency in particular weapons, and are designed for classes that wouldn’t ordinarily have them. Sometimes being an elf can help with that and the −2 Constitution is a price worth paying if it means not wasting a level in an otherwise-worthless dip, or burning multiple feats, on those proficiencies. Though for the life of me, abjurant champion is literally the only case of this that I can think of.
A few elf-only options are quite good, like the Elven Generalist Wizard ACF, or the Eternal Blade prestige class. The existence of elf races without the −2 Con penalty usually means you should pick one of those, however.
So elves sometimes do have things to recommend them, but they are few, and playing an elf is literally a cost to entry. The thing you get might be worth it, but if you could do it as a not-elf you would.
Sorcerer has very little to offer an Arcane Archer-type build, with the exception of the Elemental Affinity feature from the Draconic Bloodline origin. Combined with Elemental Weapon, this allows you to add your Cha modifier as elemental damage to every shot you fire from your crossbow. The problem here is that Elemental Weapon is restricted to the Paladin class only.
So you have 3 options, explained below. Regardless of which you take, you'll be focussing on Cha and Dex, with Con as a secondary as usual. So you'll want to spend your 27 points in the 15,15,15,8,8,8 pattern. Then Half-Elf brings you up to 17 Cha, 16 Dex, 16 Con very neatly. Each build gets you 5 ability score increases over your career. You'll want to use these to bring Cha and Dex up to 20 and take Crossbow Expert so that you can dual-wield hand crossbows.
Option 1 is to take at least 9 levels of Paladin so you can cast Elemental Weapon. Then you'll want to bring Sorcerer up to 8 and Paladin up to 12 so you don't lose ability score increases. This isn't a terrible idea, as many of the Paladin's [X]ing Smite spells work with ranged attacks, making a pretty reasonable Arcane Archer. With the Oath of Devotion's Sacred Weapon ability, you could also add your Cha modifier to your attack rolls. That said, many of the Paladin's class features don't work with ranged attacks, and it's not exactly an Arcane Archer anyway. Also, you'll have to have Str 13 to multiclass Paladin; so your starting ability scores will be 15,15,13,12,8,8 with Half-Elf making it 17 Cha, 16 Dex, 13 Str, 13 Con. (You only lose out on Con, so it's not too bad.) The main thing this option gets you that the other 2 don't is the cool Smite spells that add damage and additional effects to your crossbow attacks, just like an Arcane Archer.
Option 2 is to take 6 levels of Lore Bard for Additional Magical Secrets, which you can use to gain access to Elemental Weapon. You could use the other magical secret to get Branding Smite for that Arcane Archer flavour. Then, you'll want to take 5 levels in a martial class for Extra Attack; I'd strongly recommend Fighter, so that you can take Fighter 6 and not lose an ability score increase. Once you're Sorcerer 6/Bard 6/Fighter 6, take 2 more levels in whichever of these 3 classes you like to get your last ability score increase. This option is the least focussed, but you get the Archery fighting style and Improved Critical for your crossbow, so it's got a slight edge with the crossbow you're looking to optimize. This can also get you Arcane Archer-ing the fastest, since your combo comes into play at level 12.
The final option is to take 10 levels of Valor Bard, and use Magical Secrets to get Elemental Weapon. The other magical secret could be used for Banishing Smite, Branding Smite, or Staggering Smite for more Arcane Archer flavour. While this doesn't sound as good as Lore Bard, you get Extra Attack for free along the way. Then you should probably take Sorcerer up to 8 and Bard up to 12 to keep all your ability score increases. This option gets you the most powerful spellcasting of all of them, but you don't get the Archery fighting style.
Best Answer
OK, so, to begin: you are going to get +2 Dexterity, which is nice-ish, −2 Constitution, which sucks but at least you’ll get bonuses and d12 HD, and you will get a bunch of other stuff that barely matters at all. For reasons, you probably will not be using any traditional elven weapons (though the less traditional elven-specific weapons in Races of the Wild are solid options in a couple of cases). Thus, your elven race would be a moderately-large downside, a sort of mediocre ability score bonus, and not much else.
The solution to this is taking advantage of various elf-only options. That means you are going to need Races of the Wild, since that’s where most of them are, and Tome of Battle, because there’s two excellent things in there for you.
There are three primary prestige classes I have in mind: champion of Corellon Larethian, eternal blade, and wildrunner. They do not all work together, sadly, at least not completely, but we can still work with this.
Champion of Corellon Larethian—more knightly/paladin-y than you’re looking for, but two levels do allow you to add your Dexterity bonus to damage with certain weapons. That’s very valuable. Unfortunately, requires a stupid number of feats, too many to make workable, and the elegant strikes feature (read: the reason we care about the class at all) is incompatible with Shadow Blade (which does the same thing for a different set of weapons, and for fewer and better feats) unless you get a favorable ruling about elven lightblades and Shadow Blade.
Eternal Blade—this thing just oozes cool—it’s basically Link, Hero of Time. Furthermore, the capstone is extremely useful: once per fight, take two full-attacks in a row. You will be a crazy frenzy of blades.
Wildrunner—this is the big one, the crazy elven barbarian. It gains a “primal scream” class feature, which works very similar to rage, and stacks with that. Notably, it has a big +6 bonus to Dexterity.
Feats
Your first feat has to be Weapon Finesse. You have a bonus to Dexterity, this build relies on Dexterity, and you have to be able to hit things. What this means is, unless you have Flaws from Unearthed Arcana, you will not be able to get the Two-Weapon Fighting feat until later. Even with them, because of the feats you need to get that are not fighter-bonus-feats, with flaws I still recommend delaying Two-Weapon Fighting in order to ensure other feats on time.
If you do not have Two-Weapon Fighting, you should not attempt to use the two-weapon fighting combat option. Sorry, but you only get one feat, you are going to have to be Dex-focused, and without Weapon Finesse a Dex-focused melee fighter isn’t going to hit anything.
After Weapon Finesse and Two-Weapon Fighting, the next priority is Shadow Blade, from Tome of Battle. This allows you to add your Dexterity bonus to damage when using one of a selection of weapons—the short sword is the one for you. The issue is getting a Shadow Hand stance to use it with. This either means Martial Study and Martial Stance before you can get it, or taking a level in swordsage. The problem with the latter is it will slow down entry into eternal blade, and make its capstone impossible pre-epic.
Extra Rage from Complete Warrior is a good idea; barbarian itself gives more uses of rage only slowly.
Improved Two-Weapon Fighting can be gotten from the gloves of the balanced hand item from Magic Item Compendium. The same book has rules for adding enhancement bonuses to Dexterity to this same item without a cost penalty; obviously, Dexterity is your most important score. This build is very feat-starved, so the item makes more sense than picking up another feat. You can always pick the feat up later to replace the item.
It’s not a feat, but Twisted Charge from Complete Scoundrel will do you well.
Items
Shadow Blade only works with a select group of weapons, and you require Weapon Focus for eternal blade, so it makes the most sense to use paired short swords: they’re the best items available for dual-wielding that work with Shadow Blade. Before you get those feats, though, any combination of weapons you want to use works.
Note that Expedition to Castle Ravenloft has a sun sword, a +1 short sword that deals the damage of a bastard sword. It’s basically the sun blade without all the extra crap you don’t need; instead it costs 3,000 gp. As in, not quite 700 gp more than a +1 short sword usually would. This makes an excellent weapon to build off of; that d10 represents a +3 damage bonus over a short sword, on average. The sun blade itself is saddled with too many weak enhancements and just costs way too much money. Make sure your DM agrees that the sun sword works with Shadow Blade, too.
This doesn’t work for the OP, since he cannot use Dragon material, but for other readers: If you cannot get the sun sword or it doesn’t work with Shadow Blade, you might also consider elven lightblades, which are kind of like combo short sword/rapiers. Again, check with your DM that they are short sword enough for Shadow Blade; strict RAW, they’re not. These are exotic weapons not even remotely worth the feat you’d normally need to use them, but you’re taking a couple of levels of fighter anyway for feats, and the exoticist fighter variant from Dragon vol. 310 can get you proficiency effectively for free. Note that elven lightblades are the only possible way to have one weapon get bonuses from both elegant strikes and Shadow Blade; see the “Champion” build below for that.
Otherwise, just use short swords. The actual weapon you use is really not that important as long as it is light and works for Shadow Blade.
The gloves of the balanced hand have already been mentioned; making them double as gloves of dexterity is also an obvious priority. Also, you still do add half your Strength to damage, and your HP is on the low end, so a belt of giant strength and periapt of vitality are worthwhile, albeit at a lower priority than Dexterity. Get the best cloak of resistance generally available. Magic armor, probably angling for the fortitude or soulfire line of special abilities, is obvious. Mithral is probably your special material of choice, considering your high Dexterity.
You are going to want a speed weapon if you cannot get haste reliably cast on you. With your Dexterity, it may be difficult for your wizard to even have time to cast it before you go, and you want it for your first turn. The collision property is nice in that it multiplies on a critical hit, and various energy damage properties aren’t awful. But don’t ignore utility on your weapons; eager and warning are excellent about letting you go first, and there are weapons that improve rage or what have you, and so on. There are a lot of guides about which weapon properties you should use; this build does not have any special needs here.
Aside from that, keep up with your list of necessary magic items and peruse Bunko’s Bargain Basement for spending the rest of your money. This build does not include any built-in flight; if your alignment is flexible but your game is enforcing alignment-based rules, it’s worth being Evil just to have access to the feathered wings graft.
Barbarian 1
Your first level, your iconic level. You get rage and fast movement. You should be trading away both of these.
Rage Variant
For rage, your options are either ferocity (gain bonuses to Strength and Dexterity rather than Strength and Constitution, activate as an immediate action) or whirling frenzy (gain an extra attack). I like whirling frenzy better, but both are very solid options. Whirling frenzy will allow you to “pretend” two-weapon fighting without the feat, though.
Spiritual Totem—Lion
Complete Champion has a series of alternate class features to trade away Fast Movement for something else based on a spiritual totem. The Lion option is pounce. You need this. This is the difference from a mediocre damage build with no mobility, and a mobile damage build that is hard to pin down.
Barbarian 1/Fighter 1
Stepping aside into fighter, because you need feats. If you don’t have flaws, this is where you get Two-Weapon Fighting.
Hit-and-Run Tactics
You also take the hit-and-run tactics variant from Drow of the Underdark—you don’t need to be drow, and it allows you to add your Dexterity to damage rolls when made against flat-footed targets. That’s pretty cool, and it only costs the armor and shield proficiencies you wouldn’t use anyway. And you get +2 to Initiative, to boot.
Exoticist
This variant from Dragon vol. 310 isn’t available to the OP, but for others it may be useful. It gets you four exotic weapon proficiencies instead of all martial weapon proficiencies. You already have the latter from barbarian, so that’s no loss, and elven lightblades arguably function as short swords for the purpose of Shadow Blade. It’s a small bonus, but it’s basically free. And if you do manage to get into champion of Corellon Larethian, it works with elegant strikes, and thus the benefit is no longer anything like “small.”
Pugilist
This variant, also from Dragon vol. 310, focuses on unarmed strikes, which you won’t use much (though you could, since they are Shadow Hand weapons), but it importantly grants Improved Unarmed Strike and Endurance as free bonus feats, on top of your usual 1st-level bonus feat. It conflicts with hit-and-run tactics, and it doesn’t offer the opportunity to use elven lightblades (at least, not for free), but you need Endurance for wildrunner, so that is a pretty big deal.
Barbarian 2/Fighter 1
Uncanny dodge is nice enough. Not much to say here, class-wise.
However, it is 3rd level. Time to pick up Endurance, to qualify for wildrunner on time. Unless you went with pugilist, in which case you can actually accelerate some of your other feats. This option is best if you don’t think you’ll finish up your feats.
Barbarian 2/Fighter 2
Back to fighter, because you need feats that badly. Trap Sense is near-worthless; though Flaws can eliminate the need for fighter here, I still don’t recommend barbarian.
The feat you need here is Martial Study for a Shadow Hand maneuver. This allows you to get Hide in-class (which you’ll need for wildrunner), and you need a Shadow Hand manuever for Shadow Blade. Your options are shadow blade technique, which could easily be refluffed as a two-weapon technique, and clinging shadow strike, which gives the target a 20% chance to miss for the round after you hit.
Alternatively: Barbarian 1/Fighter 1/Ranger 2
Skills are a problem; wildrunner requires a ton of them, and barbarian and fighter are not high-skill classes. You can do well with half-decent Intelligence (eternal blade gives you a few bonuses based on it), but it’s worth noting that we’re getting Two-Weapon Fighting and Endurance—bonus feat options for Ranger 2 and 3. Thus, you can replace two levels of fighter with those two levels of ranger, which is a high-skill class (the elf substitution level in Races of the Wild even give you 8+Int!). The obvious problem is you can’t just jump to Ranger 2, so you also lose a level of barbarian as well.
We also really do want a level of fighter for hit-and-run tactics, lightblades, and/or Endurance, so trading one level of fighter rather than both, and only going to Ranger 2, is advantageous. That probably ends up being the best choice: you lose out on uncanny dodge, and an average of 3 HP (4 HP if you do take the elf substitution level, since it has d6 HD), but you retain hit-and-run tactics.
Ultimately, this works out to a lot more skills, better saves, a favored enemy, and Track and wild empathy, at the aforementioned cost of uncanny dodge, and 3 HP.
Barbarian 2/Fighter 2/Crusader 1
You gain five manuevers, a stance, and the ability to delay a small amount of damage you take for a round, gaining bonuses when you do so. Very barbarian-esque. Two of the maneuvers (or one maneuver, and the stance) need to be Devoted Spirit for eternal blade. Note that, since you’ll want to use a Shadow Hand stance in order to use Shadow Blade, your choice of stance matters only until you get that feat (which sadly won’t be for a while unless you went with pugilist).
Note that, if you like any of the 1st- or 2nd-level Stone Dragon maneuvers, now is the time to pick them up; Eternal Blade doesn’t get the discipline as an option. So definitely get mountain hammer (though its out-of-combat utility means that would be my recommendation anyway), and any others you like.
Battle leader’s charge gets a fairly sizable damage bonus (+10) on “your charge attack.” Ask your DM how pounce interacts with this; it’s completely unclear. If you cannot benefit from pounce while initiating battle leader’s charge, it’s not worth it; your other attacks should add more than 10 damage. If you can get pounce, and the +10 applies to all of those attacks, your DM is insane and this is by-far the most powerful thing you could grab right now. If I were your DM, I’d give you the +10 on the first attack, and let you have the rest as normal. Note that battle leader’s charge requires that you have some other White Raven maneuver or stance to take it.
Beyond that, I like tactical strike for a decent damage bonus if you can’t full-attack or charge, plus it lets your allies reposition, which is nice. Crusader’s strike is solid enough if you need emergency healing.
Alternatively: Barbarian 2/Fighter 2/Warblade 1
(or Barbarian 1/Fighter 1/Ranger 2/Warblade 1)
The thing about eternal blade is that it requires maneuvers from Devoted Spirit or Diamond Mind, but then learns maneuvers from Devoted Spirit, Diamond Mind, Iron Heart, or White Raven. That weird mismatch makes it very annoying for you to qualify as a warblade: that class doesn’t get Devoted Spirit, and Diamond Mind uses the Concentration skill heavily—which you can’t use while raging. You could take stance of clarity and emerald razor, which are the only two Diamond Mind maneuvers at this level that have nothing to do with Concentration. Those maneuvers aren’t bad, but probably wouldn’t be top picks for you—and to make matters worse, a 1st-level warblade only gets 3 maneuvers and 1 stance, so you only get 2 more maneuvers after those.
However, you might consider asking your DM if you could use Iron Heart and/or White Raven maneuvers to qualify for eternal blade. If you can, warblade becomes a much more serious contender: you still have access to battle leader’s charge and mountain hammer, and can also take an Iron Heart maneuver like punishing stance or wall of blades. Those are strong maneuvers (and punishing stance is very on-theme, though sadly you’ll have to ditch it for a Shadow Hand stance pretty soon for the sake of Shadow Blade), and perhaps more importantly, having an Iron Heart maneuver makes it much easier to learn appropriate-level maneuvers later when you take eternal blade.
Barbarian 2/Fighter 2/Crusader 1/Wildrunner 5
First level of wildrunner is lackluster, but you’re in! Congratulations, that’s awesome. From there, we just keep taking levels. None of the class features present options, but the primal scream feature is the big one to look for, especially the initial 2nd-level version. Hide in plain sight certainly isn’t terrible.
Your sixth-level and ninth-level feats need to be Weapon Focus (short sword is your best bet) and Martial Stance for something Shadow Hand, respectively. If you wait until 9th level, you can take assassin’s stance for +2d6 Sneak Attack damage, but the 1st-level child of shadows and thicket of blades options are both quite good as well. For that matter, the other 3rd-level stance, dance of the spider, is pretty damn cool.
Note that if your DM allows some houserules that make it possible to get into champion of Corellon Larethian, trading two levels of wildrunner for two levels of that is very much worth it.
Barbarian 2/Fighter 2/Crusader 1/Wildrunner 5/Eternal Blade 10
At eleventh level, start taking eternal blade levels instead of wildrunner levels; you have the best things from wildrunner, and eternal blade is an awesome prestige class. I suggest focusing on either Iron Heart or Devoted Spirit maneuvers, but feel free to take whatever looks cool; it will be. Avoid Diamond Mind, as it is incompatible with rage.
The feats you have left to get are Shadow Blade (finally) and Extra Rage (finally). Both of these may have been gotten much earlier if you have Flaws.
Final Build
Final Build with Flaws
Flaws dramatically improve things by allowing you to take Shadow Blade and Extra Rage much sooner.
“Starting high” Champion build with Flaws
This build has two conditions before I’d consider it:
It also relies on Dragon, which the OP explicitly cannot use.
Anyway, the idea is to use an elven lightblade rather than a short sword (or sun sword), and thus get Dex-to-damage from both Shadow Blade, and the champion of Correlon Larethian’s elegant strikes feature. That’s a pretty big deal, a much bigger deal that the sun sword’s bastard sword damage (+3 vs. something in the 15-17 range at 20th).
Qualifying for champion of Corellon Larethian remains inherently problematic, though. I’d very strongly consider whether or not I could do more with three feats than elegant strikes does. I probably could, particularly since this build can’t get hit-n-run tactics. Dodge, Combat Expertise, and Mounted Combat are not good feats. Combat Expertise doesn’t even work while using rage.
Fighter does help a lot here, though; the exoticist variant from Dragon vol. 310 gets Exotic Weapon Proficiency four times. This is important because we want to use an elven lightblade, but we also need proficiency in elven thinblades or courtblades for champion of Corellon Larethian.1 Which you choose, and what you do with the other two proficiencies, doesn’t much matter since this build relies heavily on those elven lightblades. A braid blade (Dungeon vol. 120) is probably the best choice just because it’s another free attack, though it won’t benefit from Shadow Blade or elegant strikes.
We can also add back that second level of fighter (or third level of ranger, if ignoring multiclass penalties; I tend to feel 4 skill points is well-worth an average 1 HP) to get another feat, since Wildrunner 3 isn’t exactly an amazing level.
Note that warblade is no longer an option; we need crusader for heavy armor proficiency. We have to skip hit-n-run tactics for the same reason: it prevents us from gaining heavy armor proficiency from multiclassing, we would have to actually take Heavy Armor Proficiency as a feat and we can’t afford to. Not that we would be caught dead in heavy armor (or equivalently, being caught in heavy armor would be a death sentence), but champion requires it so have it we must.
You can also delay Martial Stance until 9th, for the option of taking assassin’s stance, which opens up Craven (Champions of Ruin) for a large damage boost when you attack opponents in a sneak attack situation. Attacking with elegant strikes, Shadow Blade, assassin’s stance, and Craven is looking at +60 damage per attack (while dual-wielding high-crit weapons and only 2d6 of that damage doesn’t get multiplied on a crit).
By the way, in case that last line didn’t suggest it, a pair of scabbards of keen edge are good high-level investments. Improved Critical is fairly-obviously not a great choice, seeing how feat-starved we are, and keen is more expensive in the long run (keen is cheaper on a +4-equivalent weapon, but more expensive on a +5-equivalent or higher).
In general, crit-fishing is a fairly low-power strategy, but we have several things going for us here. We are already maximizing our attacks per round (TWF, pounce, whirling frenzy, speed or haste, island in time), we are already using high-crit weapons, and we already have a ton of unrolled (read: crit-multiplied) damage. When 16k becomes cheap at high levels, doubling our already-solid chances of getting a crit that’s going to hit ridiculously hard without us doing anything extra for chump change is a no-brainer.