Right now KDE seems to be the best for me.
Xfce is #2. Blazing fast, solid, plus run without panels it gives tons of screen space that's wasted in other wm's .
Gnome2 was always close to xfce while suffering performance issues.
Mate lacks a lot of the things that made gnome2 great: many of the little extras are now gone.
Cinnamon is not ready yet, but if they ever get it to be smooth and more easy to configure(dual monitor window list support!!) It will be very nice.
I do all my work in an LMDE VM, in my WORK vm I use a very minimal MATE which does the trick, and allows me to focus on work, not configuratons and bugs.
I never liked KDE until after the gnome 3 debacle.
Phenom II x4 955 black edition, geforce 560ti, 16gb ddr3 1600.
Mint 15 (Cinnamon edition) using KDE(xfce sometimes)
LMDE VM for work because it's portable & rolling distro(MATE)
old Mint 13 on spare partition(xfce default)