If you're new to Linux, the choice isn't really the versions - the newest versions are the way to go - just like with Windows or Mac. The real choice is which distro (Ubuntu, vs say Fedora, OpenSUSE, Mint, or Mandriva).
If you're chosen Ubuntu (it's a good choice, as are others, and it's easy for a beginner to install and use), then the real decision is which desktop you prefer. My advice would be just to try some - unlike Windows and Mac, you can install many desktops on the same Linux installation and boot into whichever you feel like at the time. It's not that any are really "better" than others - it's that one might appeal to you more than the others. Start by looking at some screenshots or videos of Gnome 3, KDE, Cinnamon, Matte, XFCE, LXDE, and Enlightenment.
That isn't an exhaustive list - but it's plenty to get you started. If you're installing Ubuntu on an older machine, go for the lightweight desktops so you get good performance. If you have a reasonably recent machine, just go with what looks good to you.