Most multiplatforms games build natively on xbox360 and then ported to ps3.That's why the performance and graphic wise is better on xbox
Not to say xbox is superior than ps3 juz that ps3 is too complex for developers to develop games as compared to xbox.
So if u are into multiplatform games buy xbox

Lol am i sound like xbox fanboy btw i owns xbox and later wanna buy pee ass 3 hehe