My Faves are X.org, XDM and WindowMaker - simple yet productive.
Personally XFeree86 is to old, KDM too flashy and ICEWM is just horrible.
GNOME is good as its like the mac or WIN2K in that its simple, sleek and fast. Its also good for people with disabilities.
KDE has more bells and whistles and looks like XP (Either a good or a bad thing)
What does everyone else think as I have had a lot of people asking me which is the "best"