I personally use W7, I have the upgrade for W8 but I don't want to deal with the headache of relearning and tweaking W8.

Performance gains are going to be fairly negligible between the two when it comes to running a game. So unless you're barely scraping by in terms of specs, use whatever you are most comfortable with.

I used to have vista and tons of people skipped over that for great reason, just wish I had done it too.