Both.
PS3 for remote play, 360 for achievements and because I play it more often and it comes out a day sooner.
I'm gamesharing the PS3 version. I probably would buy it even if I didn't, though.
Trophies are stupid. And remote play is laggy and unreliable, even if you're in the same room as your PS3, so an action game with very precise timing for swinging and releasing should be plenty frustrating on it. I can barely even play Pixeljunk Monsters with remote play..