i went with Gnome. I actually like KDE a little better because it supports dual monitors better, but i have had some serious stability issues. I am hoping gnome 3 will make me never miss KDE again.
GNOME. There's no good reason, it's just what I was introduced to and what I'm most comfortable with. KDE3 was quite nice, too, though I'm still waiting for KDE4 to reach the same level of stability (my experience with it is outdated though since I haven't really booted up a Linux install for anything other than a server for a long time now).