There's just so many to choose from...
What Pokemon would make the best chess player?

There's just so many to choose from...
Probably Alakazam. Alakazam has a perfect memory, and can essentially download information straight from the internet. It could retain and study every single high-level game ever played. It can also outperform a supercomputer computationally, meaning it is better than Stockfish 6, as a lower bound.

Alakazam, Mewtwo, Maybe Medicham, Mew, Uxie, Mespirit (Mespirit is the Pokemon of knowledge so it would know just about everything about chess) pretty much any psychic type Pokemon. But mostly just Alakazam, Mewtwo, Mespirit, or Mew. But Dialga could use Roar of Time every time it made a blunder or something and fix it, and Palkia would just use Spacial Rend on the board to send it into Distortion World when it started losing, and Mismagius could make you hallucinate so that you make the wrong move, and.... Well, you get the idea. There are tons of possibilities.
I have absolutely no clue, but if you find out, let me know how it affects your stategy :) I may git me involved in some pokemon-ery
Possibly a more interesting question is, which chess player would make the best Pokemon?

id say mewtwo or meow even he seems to know his stuff
in the articles about pokemon chess set seems like they would usually put these two as king together with pikachu, though who would be the best player, maybe also to think which trainer would make a good player, i'd put my bet on Brock.
There's just so many to choose from...