I woud say
KUbuntu, but...
I would like to argue on one point: choosing a distribution with a particular window manager in mind (or program, or configured driver) is not what I would recommend, because that way you'll always be missing something, and frustrated. Choosing a healthy and good distribution seems more important to me than picking one which provides the latest binary of your latest point of interest.
In example: I tried Ubuntu because I wanted a newer KDE than the Debian Sarge's one (I cannot download tons of megabytes from my home). Yeah, good, nice, unsuable on my system (no swap). Now I'm back to my old KDE 3.3.2 (trying to compile 3.3.5), on my very preferred distribution, Debian Sarge, because it uses half of the memory Unbuntu Dapper wastes with useless memory-consuming tools.
Choose a good sound system for the car you like, don't buy a new car each time you wanna change the radio (my opinion) !
I must say I still did not succeed in compiling 3.5.5, but once I'll do, I'll know a lot more.