I agree with everybody else: if you want if for gaming, go for Ubuntu (any of its flavours), eve if only because it's the only Linux distro officially suported by Steam at the moment.
As matze404 point out Unity, the default desktop environment in the standard
Ubuntu, is not very popular and it's got a bad reputation of hogging to many resources (which is true, but it's not the only one in giving a bad performance, and in many cases not by thaaaat much, see: http://www.phoronix.com/scan.php?page=a ... tops&num=1
). But anyway if you don't like it you can always install another one and switch over right away (there are many tutorials out there on how to do this), without waiting for the next release.
But beware! There's been some talk lately about Canonical (the company behind Ubuntu) wanting to abandon the X Window graphical server Ubuntu (and all the other Linux distros) runs on in favor of a new one called Mir. I'm not into all the technical issues at all but, as I understand it, the main problem would be losing compatibility between Ubuntu and the rest of the distros. And, most importantly from the remaining X Window-based-distros point of view, there's a real danger that hardware manufacturers (and Valve/Steam!) opt to give exclusive support to Ubuntu's new graphical server and ditch the old
X Window, relegating that distros' users to use open source drivers, which generally give a lower performance than the proprietary ones (more info on this
But again, if your only/main concern is gaming, then Ubuntu seems your safest bet in the medium/long run.