I've been using KDE lately (last 6 months). Good set of configurable keyboard controls. Works very well with Xinerama. In general, I like the configuration options. For the most part, I can get things working exactly like I want them. The designers have really thought about what kind of options people would like (though sometimes they are hard to find in all the mess). It's a heavyweight, but its meant to be that.
I've used most of the others, and used to use FVWM, TWM, and others way back in the day. I use WindowMaker in Cygwin occasionally.
KDE users will generally get flamed like we are bunch of newbies. That's too bad, because its really a good desktop environment. It gets a lot of criticism for being a Windows clone, but really it has quite surpassed anything Windows has come up with. I don't get the eye-candy argument, KDE has the crummiest look to it, and I've set it up to look simple and plain so it doesn't get in the way. But do realize that some "eye-candy" is actually visual cues that help you work faster (though a lot of it isn't).