I would go with windows 8 . But I can not stand the new windows 8 layout. I have it on a laptop and just cant stand it. Im my opinion 8 is a sh%^ operating system.
if you prefer a standard desktop layout like vista or xp then 7 is best choice. win 8 isn't as resource hungry as windows vista and 7 but it can be a pain getting used to the new layout. (windows 8 is mostly aimed at touchscreen devices, on a desktop it feels clunky without all the touchscreen swipe functions/capabilities ) --edited-- on the right hardware windows 8 is amazing, on a laptop and desktop its very awkward/clunky. on my tablet windows 8 loads in under 7 seconds from cold boot to a useable desktop!!