PLEASE INCLUDE THEM ALL! EVERY ONE OF THEM!
Please! I will end up installing them all anyway, and I switch fairly
frequently.
I use KDE primarily, because it can do anything, and it does everything. But
for my family I set them on GNOME 3, because it's so simple you can't mess
anything up. For really old hardware I occasionally revive, I use the
lightweight DEs.
For my tablet that I use for school, I switch to Unity.
Actually, the only DE I *don't* use is that default Trisquel gnome fallback
thing. It's ugly and buggy and not really good at anything (sorry!).