I like GNOME, but then again it was the first ever Desktop environment I was introduced to on Linux way back when i started off with Fedora Core 2. In truth I've only used KDE a couple of times when I was helping a friend install openSUSE on his box and it was alright, but I don't have enough experience with it to really say anything useful about it. I installed Xubuntu w/ XFCE when i found out that GNOME was too heavy for my mom's old P4 2Ghz machine (512MB ram) and that seemed to work pretty well. I managed to configure it pretty close to the way I liked with the small exception/annoyance that I couldn't get it to bind the windows key to launch a terminal. Instead it would only accept the windows key plus another key to launch something. I am sure, however, that I could probably find a program that remaps keys at the X windows level instead of the DE level, so that could probably be fixed easily. I've also played a bit with FVWM and it is really nice and lightweight, but like KDE i didn't try it that long.
Long story short, KDE, GNOME, fvwm, and XFCE are all great with fvwm and KDE being pretty good based on my short time with them.
-Zorak