I run Ubuntu Intrepid, and of the distros i have tried i love Ubuntu. I'm a newbie though, so i dont know how much weight the suggestion carries. CentOS would be my number one choice for a server but not for a user enviorment.
I would suggest you run Ubuntu and then experiment with the others via Virtualbox or a extra partiton.
One tip i learned the hard way is to make sure you install Virtualbox and not Virtualbox OSE, as OSE carries no USB support.