Hey beakersloco,
since you are just looking for opinions, here is my thoughts!
For my number 2 desktop machine(my laptop), I have been using CentOS 4.x since it was released. Of course this is also to help in the testing of SME7 stuff.
Before the CentOS, Fedora was my preferred O/S. My history as a RedHat user is pretty long which makes for a comfortable familiarity.
My testing of Linux O/S'es included all of the popular main stream distros MDK, Gentoo, Redmond, Licoris etc. before settling into Redhat. I would also suggest to try some of the *BSD variants.
You really need to just start installing systems, take the hit in "time lost" to gain your own expertise and find out which flavor you flow best with.
Good luck and have fun.
Joe