Ubuntu is the main distro, I am using it at the moment and think its marvelous!
Xubuntu, Kubuntu and Edubuntu are all different versions of the Ubuntu OS.
Kubuntu uses the KDE interface, and to me looks similar to windows 7 in the graphical effects and looks department - NOT layout.
Xubuntu uses XFCE interface. Haven't personally used it.
Ubuntu uses the GNOME interface. I think they have done well with it personally, however it is not complete without Compiz Fuzion, an eye candy addon type application.
Edubuntu is really for educational departments such as schools, however I do not know how much it is used because schools prefer windows - however Russian law says you are not allowed to use microsoft products :P
Maybe Russian schools use Edubuntu?
Anyway I think that Ubuntu is the best however I have really only used Ubuntu properly. I have used Kubuntu and do not personally like it in all, however of course there are some things they could come together on and make an orgraphsmic (graphically orgasmic) OS.
Google Images would be the place I would start, if I were you and have a look at the interface. It contributes tremendously to a happy user :D
From there, I would download Ubuntu and virtualise it on your current system using Virtualbox. If you do not like Ubuntu, try Kubuntu and Xubuntu and even Edubuntu to your liking. Fiddle around and break stuff, its fun and thats how you learn :D
Other distros you may look into are:
Ubuntu Studio
MythBuntu
A full list of official Ubuntu derivatives can be found here:
http://www.ubuntu.com/project/derivatives
shanet
PS in the source I have links to wikipedia for your further reading in case you wish to do so :D