Since I only use "windows" for game development, all my major programming, and graphics work is done on linux. But since the release of Ubuntu 11.04 I just can't stand the unity interface and have been looking at Gnome 3, XFCE, and KDE 4. I so far prefer Gnome 3 as the GUI.
Ubuntu is dead to me until they support Gnome 3 and get rid of Unity(it's crap).

So what's your favorite or current Linux distro you're using?
"I haven't decided on what distro to use for my main OS."

I recently destroyed my Windows partitions and went fully with LinuxMint 11 (http://www.linuxmint.com/) for everything. At start-up you can load either GNOME or KDE as a GUI. Honestly, after I got used to it I found it much easier to use than Windows 7.

I've been using fedora and arch linux, arch is nice but talk about stability issues..
I had Gnome 3 with arch, preferring fedora ova arch, and I must have had the quickest gentoo install ever. 1hr25min!