
Ubuntu. Me likes. Gnome > KDE. Multiple desktops for the win (bottom right, organized by function). App switcher + dictionary tool at top, system monitor and force quit at the bottom. Favorite apps top left. Very nice.
No compiz-fusion for me though, stupid radeon x1900. I bought it for gaming, but I don't even PC game anymore (pretty much because that would require me to reinstall windows, which I DON'T want to do). Oh well, everything's at least running smoothly now (except for connecting my pocket pc to my virtual XP machine, but that's a different issue...)
As an aside, if I absolutely had to reinstall windows, it would be XP. I tried Vista and liked it at first, but after a while I just got so sick of it malfunctioning. Vista caused what I actually think were software based hardware failures, something which I have never experienced anywhere else.