For those of you venturing into Howling Abyss, please...please...stop buying Sanguine Blade and thinking you're getting a slightly worse Bloodthirster. It is not a Bloodthirster, nor is it a Bloodthirster replacement. it is an okay early buy but for slot efficiency it's about where Morellonomicon is. Let's compare:
Sanguine Blade: 2275g
Essence Reaver: 3200g
Sanguine Blade: 45 + (6 per stack, max 5) (80 AD at full stacks)
Essence Reaver: 80
Sanguine Blade: 10% + (1 per stack, max 5) (15% at full stacks)
Essence Reaver: 10%
Essence Reaver: 10% CDR, Mana restoration passive
BotRK: Active slow+%maxHP nuke, Passive %currentHP shred
While Sanguine Blade is theoretically as good as either alternative in terms of damage and better in lifesteal, in the average case (3 stacks) it falls short by a significant degree. It does not build into anything and has nothing special to differentiate it. There are champions that can reliably keep the stacks up on sanguine, but that's assuming you don't have anyone like a Galio or Ziggs wiping out minions before they get near or that you have the range/mobility to consistently autoattack enemy champions without getting caught out of position. By the time you have 5 stacks, the critical stage of the fight is likely already over or you've already used your initial rotation of skills.
Perhaps the argument is less true at Plat or Diamond skill level, where I'm sure an experienced player can keep the stacks up a lot better, but...I just can't see any argument for buying it outside of gold efficiency, then selling it for a 6th 3rd tier item later.