Uematsu because, well, he's Uematsu.
Ishiwatari Daisuke has given birth to one of the best assortments of instrumental rock and power metal songs in the market.
Mitsuda is a fine composer, too. A couple of his songs were a favorite of mine in the Chrono Trigger days, though I think he was a bit sloppy and inconsistent in Chrono Cross.
I never paid too much attention to Western game musicians (mostly because I don't play Western games too much), but when I was a kid I was fascinated by the Spyro the Dragon soundtrack, composed by Steward Copeland, standing drummer for The Police.
(However, they are all overshadowed by Kanno, who has now returned to the game music scene with her score for Ragnarok Online 2
).