Hi Everyone,
Though it seems like a simple questions, the answer is not....
It mostly depend on, how cold the water should, into which you want to be thrown.
My Story:
I started my carreer in GNU/Linux about 2.5 years ago with SuSE. As I had installed WinBlows several times before, I wasn't much of a challenge. As a system, that can be installed and just works, it's fine - But if you want to installed any costum packages, you pretty fast run into the depency hell. I switched to Gentoo about 1.5 years ago, and I stayed since. I tried a few distros, but they didn't really convince me...
Slackware is great for the "Linux feeling", but it gets ugly when you want to update one or two packages - or this was my impression.
Debian sounds like a great idea, but it trashed my PC twice.... I'll give it another try when Sarge get stable this month.
Knoppix, Ubuntu, Mepis.... I havn't used them, but as they are debian based and from what I've heard, they must be great. Knoppix is probably the best LiveCD ever...
Fedora: no comment - I still have a noghtmare from RedHat...
Gentoo is a great distro, but I takes an awful lot of time to setup and to understand whats is really happening - Well I grew with this distro...
Commercial Distros: I can only repeat what has been said: not worth it! But often the best for beginners/switchers
I havn't voted yet, as I am still not sure which distro I should recomend.
Geronimo