To answer your questions:
- In your build I would take Warmog's Armor or Guardian Angel as the last item.
- I think Infinity Edge is better since it works well with Atma's Impaler
However, you cannot think like that. There is no build which is generally good. Sometimes it is better to get this item othertimes that item.
If you want a general build for Yorick I would go for this one:
- Boots of Speed + 3 or 4 health pots (4 pots - when solo top, wait near the fountain and buy 4th pot ASAP)
- Tear of the Goddess => Manamune
- probably Mercury Treads unless they have a heavy ad team, then I would go for Ninja Tabi
- straight for Atma's Impaler
- Warmog's Armor (tankier build) or Frozzen Mallet (better chasing)
- The other one of the previously mentioned items or the new item Maw of Malmortius
- Trinity Force (damage) / Guardian Angel (tanky build) / Infinity Edge (in case I have Frozen Mallet)
In case of a need I would upgrade boots before finishing Manamune, but after Tear of the Goddess. If I woudlnt be doing very well I would also get Wriggle's Lantern after Manamune or even before that and Spirit Visage, but those are items you want to sell in late game.
Early boots upgrade and Atma will give you enough resists and in combination with Manamune you will have circa 250 AD.
Finally, I think that Yorick is better with a tankier build rather than AD.
Ad NOTE: I think Nasus benefits more from a far different build. Urgot is also good with Manamune and Atma, but before Atma he really needs Brutaliser and after Atma it is better to go different items. You can also build Frozen Heart before Atma which makes you even tankier and gives you some damage, too (since you have Manamune).
Initial Thoughts
It seems like BT is the best choice if you look at it fully charged. But I'm not sure.
In terms of lifesteal - healing the BotRK returns half of the damage from its passive back.
Which means (very simplistically) that to a champion with 2k health (which is pretty medium) and NOT taking into consideration the armor (I will do the same for BT thats why I say simplistically) it deals 80 damage and you heal for 40.
The extra lifesteal of a FULLY charged BT is 8%. So that being said IF you have 400 damage (which is a lot) and the opponent has no armor you will deal 400 damage and heal for 32.
So the way I see it in terms of lifesteal, BT might actually be worse. It's also definitely more expensive and its also a kind of snowball item so its risky. You will most likely not have it fully charged the whole game.
In terms of actual damage for the same opponent of 2k health and no armor (lol)
You will get a bonus 70 damage per hit with BT and a bonus of 80 damage per hit with the Ruined King. Of course the lower health the opponent the lower the effect of Ruined King.
The only aspect that gives BloodThirster an Edge (in my opinion) is critical damage and skills that scale with AD.
When you crit that extra 70 damage I mentioned above becomes 140. The on hit effect damage from Ruined King can't crit. So if you have an Infinity's edge and a phantom dancer or Trinity Force maybe late game Bloodthirster will definitely give you more damage. (Unless you got a mundo with 4k health there.)
As far as skills are concerned it's pretty straightforward that BT gives you more flat AD so it boosts your spells more than Ruined King.
And don't forget you get the active from Ruined King too.
Final Thoughts
I totally forgot the fact that its nothing like Madred's. It uses CURRENT health not maximum. So as you can see if you have a champion with current health less than 1500. You deal less damage than BT and I'm pretty sure you're gonna heal for less as well.
That being said in combination with everything I said above, I'd go with Ruined King only with opponents that have a maximum health of over 3k.
Outside Link:
Here you can find specific numbers which pretty much draw the picture of this duel
Post Patch 3.03 Thoughts
They now changed the item as follows:
Stats
+25 attack damage
+15% life steal
+40% attack speed
Passive Unique:
Your attacks deal 5% of the target's current health
in physical damage (60 max vs minions and monsters).
Active Unique:
Drains target champion, dealing 15% of the champion's maximum
Health in physical damage and healing you by the same amount.
Additionally you steal 30% of their movement speed for 4 seconds
- 60 second cooldown. (500 range)
I like these changes a lot mainly because it no longer gets shadowed by Bloodthirster. Its now an item for a completely different purpose. If you want attack damage with your lifesteal the choice is even clearer now - Bloodthirster.
But if you want the extra attack speed and an (even better than before) on hit effect against health tanks Blade of ruined King is your clear choice. By making this item more unique I consider this a buff.
As a sidenote: After they took out Mardred's On-Hit-Effect Tanky Teemo (Malady, Wits End, Frozen Mallet, Mardred's) was seriously hit. With this item this build is back in town (not as good as it used to be with Mardred's but still its nice to have the option to play it)
Best Answer
The new Patch changed ADCs Completely. Before this patch Bloodthirster was basically the only thing to buy on an ADC with very few exceptions (Vayne, sometimes Twitch). Now you have 3 Main Options to rush. Bloodthirster is actually none of them.
Why is Bloodthirster a bad Choice?
BT is just more of a defensive Item right now. It's a lot more expensive and it has lost its stacking power. The reason BT was so strong is because if you had The item and your lane opponent just had the components, you would still deal a lot more damage just by stacking it up. Also if you forced your enemy out of lane before he could buy a BF Sword you were in a huge advantage if you got one yourself. I guess Riot wanted to rebalance this by giving you more opportunities for building a core. You shouldn't rush BT under any circumstances I could imagine right now. Maybe you shouldn't even buy it at all.
Dignitas did a gread job at calculating how the new Bloodthirster competes against the BotrK.
Now for the rest I think you can imagine that Infinity Edge is a lot better than BT (300g more and +25% Crit, +50% Crit Damage). Basically on "Burst ADCs" like Lucian, Graves or Corki you should be rushing an Infinity Edge. Of course we shouldn't forget about the new Item (Essence Reaver) . While this Item may seem a little odd on ADCs at first it's a really strong thing to rush on a few ones. Especially Lucian, Urgot (Yes I'll put him here although noone likes him) and Ezreal wil profit a lot from the Mana and CDR. Also it's easy to build since you it's key components aren't expensive.
On pure autoattackers (Ashe, KogMaw, Twitch) BotrK will be the best choice to rush right now. It got buffed a lot for ranged champions while it was slightly nerfed for Meeles (+3% On-Hit dmg, -5% Active dmg). When playing some kind of Hybrid ADC (Varus, Jinx, MF) the Item should be Situational If you want to Push and Duel early you should probably go for a Blade while IE would be better in Teamfights.
So basically:
TL;DR