My primary WM is XFCE. I use XFCE primarily because of xfce4-panel and terminal.
I will also use Fluxbox when I need a "minimal but usable" WM on a system where I don't want a lot of extraneous things installed, but need an X application. I have Ocicat to thank for introducing me to Fluxbox.
I have an Ubuntu partition on my laptop for some Linux-only apps, and use the default Gnome. I used to have Xubuntu installed, but switched because Xubuntu has Gnome libraries and applets installed anyway, so it may as well
be Gnome, and Ubuntu was easier to adminstrate than Xubuntu.