Thought Vessel v. Skullclamp v. Solemn Simulacrum
EDIT: Meant Thought Sponge, not Thought Vessel.
Basically title. Of the three, which would you pick and why? Or which of the two?
[[Thought Sponge]] can easily net the most cards over the course of a game. Once your engine is online, it can result in 8+ cards per turn cycle. It can also generate its own +1/+1 counters.
[[Skullclamp]] is classically the most powerful, but it can feel awkward to pay one to equip, which you can only do on your turn. Also the least intensive mana-wise, but not a creature that you can bounce once the engine is going.
[[Solemn Simulacrum]] is ramp and card draw, and is colorless. Sad robot also synergizes well with modular cards. On the other hand, you need to run enough basics to justify running him.
FWIW, I run a Nazgul build of MTBR and am trying to optimize. My card draw suite feels pretty good, but I'm trying to decide which of the above two make the cut. On the fence about cutting [[Mikaeus]] and running all three.