Cut my teeth on Fedora Core 2 and 3 back in late 2004. I used Fedora exclusively until August 2005. Switched to Ubuntu Server on a whim in October 2005 because it was the newest distro at the time and the only one which supported NVIDIA SATA. I really
liked the Debian style package management and the vast amount of packages so I installed it on my desktop machine, too. Around June 2006 I lost some of my enamoration with Ubuntu 6.06 due to hardware issues and went SUSE for the summer. With 6.10 I'm back
to Ubuntu and looking forward to 7.04.
On the UNIX side, I've used Solaris at school and AIX on an RS/6000 I have. I've barely touched Tru64 and HP-UX. Of the four, AIX is probably my favorite. I like smitty a lot. Dabbled with the BSDs but haven't used any particular one long enough to have much
of an opinion.
On the fringe, not really Unix, but POSIX compatible, is OpenVMS. I've run that on emulated VAX as well as a real Alphastation and I think it's pretty cool, but I'm not nearly as comfortable with it as I am with Linux/Unix, although I'd like to get better with