Im running Vista x64, i love it, but then again i dont blink at buying a new video card or 2, as i bought myself for xmas, I cant compare the 2, simply because i havent usd XP for so long its not funny, apparently theres a thing called 'vista lag' in games, ive never noticed this myself, but as i said, im currently running 2 8800GT's.
The only thing i can say for sure is, if your going to go Vista, go 32bit. Unless of course your systems runs a quad core and 4gb ram.
Personal preference, i love vista, i find it easy to use and responsive, i like the feel of the OS. Once you turn off all the security alerts and UAC (user account control) it runs very nicely.
If your system is pretty new, you'll never have to go searching for drivers again, finally windows update is useful!