KDE and XFCE... !!
on KDE , I can use every application available (also for Gnome and XFCE) but on Gnome and XFCE I can't run all applications for KDE (superkaramba for example).
on XFCE, I have some sort of simplicity which can be beautiful but only when the graphics are great.
for KDE , I use SabayonLinux.
for XFCE, I use Dreamlinux.
Those are the only systems on my harddrive.
The reason why I like Sabayonlinux AND Dreamlinux so much together is because they both offer a complete out of the box experience for multimedia/java/flash/codecs etc and they both offer Beryl out of the box now.
Still, I use KDE the most so I boot with Sabayon the most.
I also have tried Elive because they use the "E16" or "E17" desktop environment.
They did a great job , a really great job, but I still don't like Enlightment.
I've used Gnome on Ubuntu but I don't like it... some like Gnome, some don't, I don't