This winds up getting away from the idea of the hulking thug rogue/barbarian; the solitary barbarian level is used to grant mobility and agility rather than strength and endurance. That said, this is a very vicious combat build with lots of dirty tricks, very capable of pouncing on opponents unawares and tearing into them in an unholy frenzy.
The Assassin
For a low-optimization, low-magic campaign, where you want to focus on stealth and skills but still be able to deal the hurt, you could do a lot worse than the core assassin prestige class. It gets a number of low-level spells, so it should not be a problem for low-magic, but if there’s little magic available, you definitely want what little you can get.
If alignment is an issue, consider the avenger: it replaces the Evil requirement with a Non-Chaotic requirement, which is often much more amenable to characters.
Spells
Spells are the reason you go this route. The assassin spell list is quite solid, for as small a list as it is, and it will likely fly well in a low-magic game.
This recommendation does assume that you have access, at the least, to Spell Compendium. The core assassin spell list leaves a lot to be desired. If you want to use the avenger, also make sure your DM is OK with adding the Spell Compendium assassin spells to the avenger list. That’s in line with the guidance in that book for non-core spellcasting classes on pg. 3, so it shouldn’t be a problem, but it’s a conversation you should have.
Psionics
The psionic assassin from Secrets of Sarlona also exists, and adds the very interesting option of using Expanded Knowledge for psionic minor creation, which is an excellent way to get poisons. That said, unless your DM allows other assassin spells to be converted into psionic counterparts, it’s not a great option. If you can, then you might as well?
Death Attack
Don’t focus too much on Death Attack; at best you can attempt it during a surprise round after spending three rounds studying your target out of combat. Attempting to hide and wait three rounds mid-combat is always a bad play.
Poison Use
Poison Use is meh; if you want to use poison, you want the Master of Poisons feat from Drow of the Underdark anyway. That said, Master of Poisons is a quite-solid feat, and Craft (poisonmaking) can get you poison at a huge discount (if you have a source of materials, ⅙ market price). Poisons provide a way to apply debilitating effects along with straight damage. See the Arsenic and Old Lace handbook for more details if you’re interested in going for poisons.
Again, if you are avoiding being Evil, you have to clarify something with the DM: poisons, according to Player’s Handbook and Dungeon Master’s Guide, are not evil, though usually illegal (and always dishonorable, which is why they are barred to paladins). Book of Exalted Deeds, however, says they are actually Evil – and then gives a definition/explanation of how and why they’re Evil that would include, for example, the natural poison of the couatl, that is, a notably Good creature. Book of Exalted Deeds is not a good book. Just make sure, if you don’t want to be Evil, that your DM agrees that Book of Exalted Deeds is stupid, and poisons aren’t any more inherently evil than swords.
Hide in Plain Sight
It’s a long time coming, but getting Hide in Plain Sight, along with taking the Darkstalker feat from Lords of Madness, will prevent a lot of the major ways to simply shut down your stealth. Highly recommended.
The Black Dog
This prestige class from Dragonmarked stacks with assassin levels for Death Attack DCs, and has a couple of excellent abilities aimed at poison. I’ve decided that poison is a good direction to take this, hence its appearance here.
The black dog requires the Mark of Hospitality feat, which in Eberron is limited to halflings. This is a matter of setting fluff, so if you aren’t playing in Eberron, the Mark of Hospitality might be available to half-orcs. On the other hand, I actually like halfling a great deal more than half-orc here. It does mean a shift from Strength to Dexterity which you may find undesirable, but half-orc is quite weak, and the halfling’s size is basically all to your benefit (average of −1 on damage rolls, but +1 attack, +4 to stealth, and +1 to AC). The existence of the strongheart halfling (Forgotten Realms Campaign Setting) really seals that deal.
Suggested Build
Strongheart Halfling Rogue 3/Barbarian 1/something 1/Black Dog 5/Assassin 10
At Rogue 2, the Penetrating Strike alternate class feature (Dungeonscape) is key, and at Barbarian 1, you really want the Lion Spiritual Totem alternate class feature (Complete Champion) to get Pounce instead of Fast Movement (you’re not a charger per se, but you do want to maintain mobility and full-attacks, and pounce is a really good way to do that).
I’d replace Rage with Ferocity, though I’d also consider Whirling Frenzy.
The something 1 I’m not sure about; barbarian 2 is OK but not great, rogue 4 is fairly mediocre...
Some options that should be no problem:
Fighter. You want Weapon Finesse at this point, so that’s a use for your bonus feat, and the Hit-and-Run Tactics alternate class feature from Drow of the Underdark trades some armor and shield proficiency you probably won’t use for +2 to initiative and Dex-to-damage vs. flat-footed foes, which is awesome.
Ranger. Simple: full BAB and 6+Int skills. Boring, but functional.
Anything that gives Sneak Attack +1d6 at first level. Again, boring, but functional.
Some options that probably aren’t allowed, but could be awesome:
Cleric. Best single-level dip in the game, bar none. Could be worth it even if you get none of its spells. Domain granted powers are awesome, and failing that you can trade them for Devotion feats (Complete Champion), many of which are excellent. Turn/Rebuke Undead is excellent for Divine feats, including the amazing Lolth’s Caress (Drow of the Underdark). While a halfling who worships Lolth is weird, with this build’s interest in poison it’s not a stretch to worship the goddess of spiders. Or if Lolth doesn’t exist in your setting, maybe you can just ignore that requirement.
Ardent or Psion. One level is sufficient to manifest psionic minor creation, which will get you a plant-based poison that lasts an hour. Not a bad deal at all.
Swordsage. Cloak of deception provides instant flat-footing for an enemy, once per encounter, while shadow jaunt provides great mobility. Wolf fang strike and sudden leap allow you to continue to dual-wield effectively even when you’re forced to move and cannot charge. If you later take Martial Stance, you can snag assassin’s stance for +2d6 Sneak Attack damage.
Anyway, you definitely want the Craven (Champions of Ruin), Darkstalker (Lords of Madness), Master of Poisons (Drow of the Underdark), and Weapon Finesse feats. Plus, black dog requires Mark of Hospitality (Eberron Campaign Setting).
The feats Extra Rage (Complete Warrior) and Wild Cohort could be very nice for you, if you can squeeze them in (maybe later, or if you take a Fighter level and have another feat to play with). Note that I don’t recommend Wild Cohort so you have a pet fighting alongside you: I recommend it so you have a reliable, cheap poison dispenser following you around. Unfortunately, both feats are kind of lackluster by the time they fit into the build I am proposing.
Anyway, your feats may look like this:
- Bonus racial feat: Weapon Finesse
- 1st-level feat: Master of Poisons
- 3rd-level feat: Mark of Hospitality
- 6th-level feat: Darkstalker
- 9th-level feat: Craven
- 12th-level feat: Extra Rage?
- 15th-level feat: Wild Cohort?
With this combination, your attacks hit hard, and you are hard to find. You have poisons that you can use selectively, and they are very dangerous. You have a smattering of spells that will make a huge difference in a low-magic world. Seems like a pretty solid approach to me.
Best Answer
Your question revolves around the mechanical quality of various options, and I will therefore give an optimizer’s perspective to the issues. I will use words like “should” or even “must” without qualification, so I am stating up front that this entire answer is qualified as applying if you want to optimize your character.
Unfortunately, your question of regular fighter vs. sneak attack thug is problematic. Because of the realities of 3.5, which favors heavy multiclassing for martial characters, this is a false dichotomy. Thus, I’m going to introduce my answer with a significant tangent into metagame theory surrounding the fighter class. I consider this critical background information to discussing the sneak attack thug.
Why take fighter levels: Feats and BAB
The fighter is a weak class; feats are all he gets. Feats are valuable, but class features are (or should be) more so. The fighter is also a full-BAB class, which may matter to you but may not. Generally, these features are most critical when it comes to qualifying for prestige classes.
Bonus feats
In core, there simply aren’t enough feats that are good enough to justify getting only feats as your class features. Outside of core, there are more than enough feats, but the alternatives to fighter get that much better. In other words, (the regular) fighter is a class you only take if you are desperate for feats and cannot lose any BAB (if you can lose BAB, cleric, monk, and psychic warrior are often more effective ways to get feats).
The only time you should be “desperate” for feats is when you want to use a prestige class that requires a lot of them.
Base attack bonus
As for BAB, it’s important but not the be-all, end-all, unless you’re aiming to enter a prestige class that has BAB as its primary “gatekeeper” (that is, you can enter the class as soon as you have enough BAB, so missing out on BAB directly delays entry into the prestige class). If you want to enter a class that requires BAB +3, but 8 ranks in a skill, missing some BAB won’t matter much because you wouldn’t be able to enter until you got the 8 ranks anyway. On the flip side, if a class requires BAB +5 but 4 ranks, missing a BAB puts you a level behind, which is a fairly big deal.
Conclusion
So ultimately, fighter is a class that is best used to ease entry into prestige classes. In low-level games, where feats are more scarce, two levels (for a feat per level) can be good, too. But usually, you get enough feats to get the ones you actually want without needing fighter levels, which means those levels are better spent elsewhere.
Reality: fighters multiclass
Because fighter levels are primarily useful for entering prestige classes, it almost goes without saying that fighters should not literally be Fighter 20. In reality, they shouldn’t actually be more than Fighter 2 most of the time; a feat-per-level is solid; a feat-every-other-level is not. But most prestige classes cannot be entered at level 3. Thus, you need other classes.
Multiclass Penalties
Most groups do not use multiclass penalties; they are ineffective at doing what they were intended for (limit multiclassing) and many groups feel that was an undesirable goal in the first place (multiclassing is one of the biggest strengths of the d20 system).
That said, as a Fighter 2, you don’t have to worry about it. You do not suffer multiclass penalties as long as all your classes are within one level of each other, which means you can be Fighter 2, Fighter 2/X 1, Fighter 2/X 2, and Fighter 2/X 3 (or Fighter 2/X 1/Y 2 or whatever) without any multiclass penalties. Prestige classes also do not count, so if you enter a prestige class at 6th, you’ll never see a penalty.
Typical options: barbarian, cleric, ranger, warblade
Barbarian and cleric are two of the best single-level dips in the game. Barbarian 1 gives Rage, and with Complete Champion, Pounce. Cleric gives a smattering of spells, two domains (which may mean two bonus feats, or things you can’t get as feats), and Turn Undead which can be used with Divine feats. Complete Champion again improves that option, adding the excellent Devotion feats as alternatives for Domains, including the fantastic Travel Devotion. Because of Pounce and Travel Devotion, basically every melee character ever should have at least one level of either barbarian or cleric if Complete Champion is in play.
If fighter is your choice for entering prestige classes that require a lot of feats as well as BAB, ranger is your choice for entering prestige classes that require a lot of skill ranks as well as BAB. Full BAB and 6+Int skills is solid. The actual ranger class features are fairly meh, but if you need any of those feats, hey, more free feats.
Warblade from Tome of Battle is an excellent class, and it multiclasses very nicely (half your non-warblade levels count towards your warblade level for the sake of the warblade’s maneuvers). It’s often seen as “what the fighter should have been,” but if you need a bunch of feats, taking fighter levels before entering warblade works quite nicely.
Sneak Attack Thug and Rogue
What I’ve established, hopefully, is that you should not compare a Sneak Attack Thug 20 to a Fighter 20; neither option is likely or desirable. Rather, you’re talking about a Fighter 2/something 3/prestige class 10/another thing 5 or something, and wondering how the sneak attack thug fits into this picture.
Some basic facts about the sneak attack thug
The Sneak Attack fighter is better in combat than a (core) rogue. He arguably gets 1d6 more Sneak Attack (thanks to the bonus feats on both 1st and 2nd level), he has full BAB so iterative attacks come online sooner. The thug is more skilled than a regular fighter by a fair margin, though far, far less so than the rogue.
But ultimately, the Sneak Attack thug’s only schtick is combat, and there are better ways to do combat than Sneak Attack. Simple example is a mounted fighter/barbarian charger with a lance and Power Attack. Another good one is the so-called horizon tripper, taking advantage of Improved Trip’s excellent lock-down by using Combat Reflexes, and comboing fighter, barbarian, and ranger in order to enter horizon walker for excellent mobility.
Considerations of the rogue
Meanwhile, the rogue is generally seen as a higher “tier” class than the fighter. In combat, the class is lackluster; Sneak Attack is non-trivial to set up, relies on feat-intensive dual-wielding for optimal damage, and even with all that it doesn’t keep up, damage-wise, with a good charger.
But the rogue is still better. All a charger can do is damage; a rogue can do so much more. The thug adds in a fair few more skills, but the class skill list is still paltry compared to the rogue’s, and the rogue probably has more than twice as many skill points. Most importantly, the rogue gets Use Magic Device in-class, and that skill is amazing.
Conclusion
If you do not need feats very badly, you don’t really want (regular) fighter levels. The sneak attack fighter replaces these with Sneak Attack; not a bad trade, but the rogue gets so much more along with Sneak Attack.
So you should only take fighter levels if you really need BAB and feats or Sneak Attack. If you’re a rogue, stick with rogue unless you need BAB for something. If you want some BAB, but aren’t hurting for feats, a sneak attack thug level will get you BAB without costing you Sneak Attack, and it’ll hurt your skills at least somewhat less. If you really need BAB and feats, then regular fighter is your best bet.