There are detailed comparisons here
http://www.trustedreviews.com/opinions/macbook-pro-vs-macbook-air
but I'm wondering what type of games you want to play? There are far, far more games available for Windows machines (or, indeed, for Android devices) than there are for Apple laptops. I can't really see where you'd benefit from buying a MacBook. (Even at secondhand prices, you'd still be paying perhaps a couple of hundred quid above the price of a comparable Windows machine, with fewer games available).