First of all, if you have more than 4GB of RAM and you want it all to show up, Vista Ultimate 64 (which I use), or XP 64-bit edition are your only options. The only reason I chose Vista over XP is because I have 10GB of RAM and I wanted to get the Windows OS of the future, which there are more and more games popping up that are solely compatible with Vista. I know most people say XP is more stable, and that may be; however, I have not had any problems whatsoever with Vista 64 other than the annoying UAC. As of right now, most games are Vista compatible, but not 64-bit compatible.
If you don't have over 4GB of RAM or do not plan on it, I would recommend the Vista 32 Premium. If more and more games are coming out Vista only, then why buy an OS twice? I have yet to spend much time since service pack one, but if what they claim is true, performance of gaming is almost side by side with Vista and XP. I am not a Vista fanboy, I just picked the one I felt would last in the long run.
If you don't have over 4GB of RAM or do not plan on it, I would recommend the Vista 32 Premium. If more and more games are coming out Vista only, then why buy an OS twice? I have yet to spend much time since service pack one, but if what they claim is true, performance of gaming is almost side by side with Vista and XP. I am not a Vista fanboy, I just picked the one I felt would last in the long run.