Centos (who cares about RHEL) needs a bit more extra work to make it more useful for desktops. I had to build me own kiosktool rpm for example.
Ahh, yes. RH has pretty much said they're not interested in the desktop market. Until that changes either Fedora or Ubuntu it is. I'd pick Ubuntu too probably. Just "works" outta the box with a lot more things your average desktop user demands.
Disclaimer: I use Fedora on all my desktops. ;)
Ray