Knowing little to nothing about Linux, I picked Fedora. The GUI made the initial migration pretty painless. There were some bugs (in fact there still are), but I like the feel of it. I can pull up the command line in Fedora and it's similar to using the DOS interface in windows. Actually I like it better than DOS. It feels more workable. I picked up the basic commands pretty quickly.
Of course I'm a newbie to this stuff to so my opinion may not warrant a lot of attention.
I've also heard/read good things about Red Hat Enterprise and have considered putting it on another machine to see how it drives. However, being generally cheap by nature I have remained with the free Fedora.
Of course it all ends up like when you pick a new car. You gotta test drive it before you know.