I'll try to summarize what I've learned over the past 13 or so years that I've been using Linux.

Debian - Rock Solid, sometimes a bit old, but always stable. Would recommend running Testing if you use it as a desktop system. Good for customization.

OpenSuse (previously Suse) - Never have liked it. Seems fine if all you do is install it, but don't want to add anything new or use anything except the included software.

Ubuntu - Debian based, but as said before doesn't follow all of Debian's "It must be free, damnit!" philosophy. Also has a better initial setup than Debian, and the project goals have always been to have the latest Gnome.

Arch Linux - Can be a bit bothersome to set up, but once it's there, it's quite a magic distribution. Awesome if you MUST have the latest software.

Slackware - In as much as I have been meaning to, never have tried this oldie, but goodie.

RedHat (Or CentOS) - Rock solid, just like Debian. Good for Servers, not so much for Desktop.

Fedora - This is the real bleeding edge, even more so than Arch. Fedora is like OpenSuse in that it is the 'testbed' for RedHat and OpenSuse is the testbed for Novell Suse. But it seems that more innovative technologies come from Fedora first (Network-manager, pulseaudio, etc) Has far too many growing pains for a new user.

Mandriva (previously Mandrake) is a fairly nice built system, though it is like OpenSuse in that if you install too many things outside of the default repositories, you're looking for major breakage. Also stay away from cooker packages.

As far as installing one version and upgrading to the next, you really can't beat Debian and Ubuntu. I've successfully upgraded my mail server fro Debian Sarge, to Etch to currently Lenny. Yes, that's about 5 years of never re-installing, and that's even through a hardware change or two.

Ubuntu a little less so than Debian, mainly because of their 6 month release schedule, and they don't have as much time to make sure upgrades are clean. But still, they are a debian base... I've never seen any that can touch it (with the exception of CentOS / RedHat that have been able to upgrade versions, but then it was only minor versions (5.2 up to 5.5 was pretty smooth))

Good luck, and welcome to the awesome world of Linux.

slaapliedje