For a newbie, definately Linux Mint or Sabayon for what comes out of the box, and how smooth the transition is. It will take some time before you say "oh, my Linux broke, and I don't know what to do!" Sabayon has most of the functionality as Linux Mint, and is a very mature and stable distro, based on Gentoo if I am not mistaken.
As for the more stable of the two, it is Gnome - which can be made to look well too - there are misconceptions that it is a dull and boring DE - case in point, is again, Linux mint. KDE is also great, and a wee bit more user friendly. Have used three of the four distros you listed, and this is where each of them will break:
Ubuntu - the codecs, you cannot play mp3s out of the box, and the interface suffers from strange glitches - not bugs that are predictable, but random glitches that just go a little haywire now and then.
OpenSuse - the package manager is a little buggy, but the one click install is convinient - about half of the time that it actually works. Easier to get codecs installed here - because of a very prominant and easy to follow tutorial, but still does not play anything useful out of the box.
Fedora - Great to start learning some of the advanced stuff right away, but you will have to spend some time with it.
If you want a plain and direct answer, definately go for Linux Mint, you will not be disappointed. It is Ubuntu minus all the quirks and difficulties for noobs (please do not misinterpret the word).