Yeah, I would agree with Bob and say that the early composers from Baroque and back have some of the least pianistic music, simply because they wrote with their instrument in mind, not our instrument, which has changed very much over the years. Many modern composers (I could name many, after the obvious ones like Schoenberg) also have very unpianistic music, simply because they think more about the compositional processes in the music than making it a pianistic work. I know this firsthand, having worked with composers who have written works for piano. The major common practice composers have unpianistic works, but they can't hold a candle to either early keyboard composers or many modern composers.
As for the most pianistic composer, I would argue that Chopin and Beethoven have been the most pianistic for me, but that is subjective.