I would say Pro. I have used it now for over 2 years with my gaming and i have never come across a problem. While Home doesnt have all the features of Pro.
Gaming doesn't matter whether you use Home or Pro. They both are the same OS as far as games are concerned. Pro just gives you a bit more customizability so you have more tweaking options which in turn could increase gaming performance.
XP pro, Havent had any major issues with it except the occasional lockup which is normal other than that no problem. But As Beedubaya says doesn't really matter same difference really