Definitely 7. Got it on my shitty laptop which I basically never used and don't have anything on it (not even a desktop wallpaper). I only use the laptop to try out 7 (which I really liked). But my main PC (a desktop) has XP, which I have stuck with ever since it was released. Vista basically a downgrade of 2000. Hundy don't even get me started on Macs, I mean they are just the shittest thing possible (worse than shit itself).