There has been chat about innate ability and learnt ability. I always liked the Capablanca - Marshall game, where Marshall uncorked his gambit (although it has been said that it had been played before).
However, I really do think that Capa was presented with a problem over the board - which he accepted, rose to the challenge, and won. I think that this is an example of innate ability.
Perhaps there are more games like this, where a chessplayer has perhaps been 'found out' as it were by failing to adapt to new ideas on the board. Any suggestions anyone?
So, I'm going to go for Capa :)
I'll vote for Magnus Carlsen.