Ubuntu is a good one for a desktop OS. Fedora is likewise pretty good; it just isn't the darling of the media for whatever reason, probably because Red Hat's focus is enterprise. After a hiatus away from Linux for the past two years, I recently came back into The Fold and tried Ubuntu, but had issues in the the installer wouldn't recognize my SATA DVD-ROM drive. Ended up with Fedora for that reason.
Pick one of those two distros; they'll usually have up-to-date repositories of software, which is both the best and worst thing about Linux: dealing with the picayune differences between distributions.
As for game development, Linux is currently a bit... well... not dead, but certainly not as easy as in Windows, unfortunately. First, those picayunes rear their ugly head in a bigger way when developing games. Second, the market is still dominated by techies who don't play a lot of games, although the gaining desktop share should help that. Third, IMNSHO, the libraries are not as available or documented as in Windows. It hit a peak a while back (2000-ish), with some game shops like Loki trying to create a market, but that died somehow. As a counterpoint, it is certain to pick up pace again as Linux makes gains on the desktop.
As for Windows being too slow, being a "jack-of-all-trades" OS comes with a cost, and it does a lot behind the scenes, but can be trimmed down. Lots of services, program launchers (TSRs really) and updaters chew up memory and CPU cycles. You'd be surprised what a good pass on Process Explorer + Autoruns can do for you, when coupled with Blackviper's guide tips too.