I Like Gnome 3 quite a lot. I just fits my work habits really well:
* Alt+Tab (and Alt+Key-above) works just as I really want them to work. Perfect
* Dynamic virtual desktops concept is perfect for me
* Minimalistic look. I really hate when toolbars are full of icons, and every place is full of things.
* Desktop overview is good & easy (or whatever it is called, where you can manage your windows, and launch new programs etc.)
I have only few problems with Gnome 3 - one being that gnome-tweak-tool should really be included by default.
My second favorite is Awesome window manager. I've also tested Xmonad and Kde quite extensively for several weeks, but Kde is way too "stuffed" and confusing for my tastes, and Awesome seems to be better fit than Xmonad for some reason.