Windows 10 is the newest and I heard it's the overall fastest when it comes to games. There's a little controversy about it "spying" on you. But there's a download that takes care of that for you. Windows 8 isn't very good compared to Windows 10, and Windows 7 is a lot of people's favorite, but it's hard to find new.
Personally, I say Windows 10 if you're given the option. It seems to a boost in FPS compared to other versions. Vista and older versions are severely outdated and are definitely not recommended.