I know this will put me squarely in the "geek" column, but my preference is debian (
It's not for the newbie, as it doesn't have a flashy installer and expects that you have some knowledge coming into things. But if you know what you're doing, you'll probably be happier with debian. dpkg is a much better package manager than rpm and the packages *work*.
I ditched RedHat years ago when I got sick of perl not working right (RedHat 4.x and 5.x had perl built poorly, I always ended up rebuilding from source). When I first was using it, I didn't mind because I was a young system hacker who enjoyed rebuilding things from source when the rpm sucked and didn't mind that the kernel that shipped sucked because I'd just rebuild a new one. Now, I want the system to work because I have bigger and better projects to do, so I want packages to work, I want a decent kernel shipped, etc, etc. A friend recommended that I "grow up and move to debian". Tried it, loved it, and have stuck with it.
debian has three systems available, stable, testing, and unstable. Stable will get you a very stable system due to things being tested and not bleeding edge. Testing (what I run) is also very stable but has more bleeding edge software in it. Unstable is the build-of-the-day version that can be unstable, but hearing from people who run it, rarely has actual problems. If I was running a server, I'd use stable unless I *needed* something better. As a developer, I run testing.
RedHat is notorious for bad decisions like that. Not so long ago, when they decided they wanted to upgrade gcc, they just went and grabbed the latest development cvs tree of gcc (that's right, devel, not release), built it and put it in their release. The gcc developers tossed a significant part of that tree, leaving RedHat with an incompatible version. Bad decision making that seems to be their trademark. In the end, RedHat seems to be like Microsoft -- the market leader for no discernable reason.
SuSe - Great desktop system.
Mandrake - Based on RedHat, so has some of it's faults, but much more stable due to lagging behind and not always following RedHat's bad decisions (see gcc above).