I'm using KDE (Slack 10) for the following reasons:
- It's the most "Windows-like".
- It has almost ALL programs installed on its menu
Drawback: It's the heavier desk. manager I ever used. (But no TOO heavy).
I gave up on GNOME because its menu had only GNOME apps. (Ok....I'm lazy....

)
I tried XFCE but I didn't like the documentation (I'm without internet at home for a few months.)