I use to think Windows XP was better because everyone was saying "oh Vista sucks, it's slow, it's too complicated" and stuff, then I realised, well, the people that said that were the ones that didn't know much about computers.
I use to be a Microsoft fan, then an Apple fan.
But out of XP and Vista, I'll probably say Vista, but it is a close one.
Honestly, if Vista is too slow then you just didn't spend enough $$$ on hardware.
1st - Vista (just by 0.000001)
2nd - XP
3rd - Linux/Unix based OS'
4th - Mac
I hate macs.