I'm surprised most posters seem to go cinnamon or xfce. I used to use cinnamon all the time, because you can make it look nicer. I'm sure it's improved alot but it was buggy and I prefer a stable system to a beautiful system. Saying that, aesthetics is important, and I just didn't like the look of xfce out of the box... I like to do complete reinstalls rather than upgrade (again, makes it less prone to problems) and this means I just don't want to spend a week messing with the desktop and file manager to look nice... Especially as I have it on 3 different systems.
For me MATE has good reliability, any tweaks I want to make it look beautiful take less than 20 seconds (dark theme, change wallpaper). I DO miss the flexibility that nemo would provide (eg more locations to copy to) but opening the usb window is worth the price of trusting in its long term stabilitt and having a nice menu system that to me is pretty and clean.
Please post suggestions for improvement of Cinnamon here