Hmmm... my pick isn't on the list...
I'd say Scriabin.
His early piano works brought a brand new way of voicing music into the genre... and his later works brought about an entirely new tonal system that no other composer has been able to match, or even imitate.
... Although I suppose my 2nd pick would have to be Bach. He was really the father of it all. Without the Well Tempered Clavier, Mozart's and Beethoven's works would have been nothing. Mozart only brought new polyphonic depth into his music because of the Well Tempered Clavier, and Beethoven also studied it himself...
... But Scriabin is still my #1 pick.
