In my limited experience with *nix OS's, I think the distro you choose comes down to how 'techie' you want to be. If you just want a simple to use OS with everything available via a GUI and a large community for support then it's hard to go past Ubuntu.
That was its MO, and if you're not running a server it's more than capable enough and has a huge application repo for installation via the GUI package manager (it's easier than Windows!).
The underlying kernel is basically the same in all *nix systems, it's how many bells and whistles they install as standard that makes the most difference.
Another option to take different distro's for a spin is install VirtualBox or VMWare and download a few and run them in a VM on your current Windows, it's quick and easy.
I'm doing a CLI tutorial atm and they provide an image for use in the course which is Ubuntu so if you want to learn/brush up a bit on your CLI it seems like a great tut.http://www.learnenough.com/