I'll get XP for my own pc also, Vista piss me off.
Vista simply doesn't work
Win 7 is also slow and has some incompatibilities
Is ok - works stable and not that slowly.
But for me all of them suck: since I have my new graphics card and monitor I cannot really play online: It the graphics card gets too warm on high details and then the computer crashes. Even my monitor crashes and restarts after that.
I don't know why, but on Linux I never have these problems
So the winner is...