This question has been asked before, for example in https://news.ycombinator.com/item?id=5730762 but that was more than two years ago, and it would be interesting to see if there are any changes.
Fedora 22 with KDE Plasma. Works great for me. The repositories have damn close to everything I ever need, especially if you add the RPMFusion repos. And with the latest kernel upgrade that came down, it works surprising well on a pretty wimpy laptop, even running heavyweight Java apps like Eclipse and JBoss. And now that I committed to switching back to KDE (I used to use it, then got away from it for a while) I'm really falling in love with KDE again. This is fairly close to a perfect desktop experience to me.
Isn't Mint one of Ubuntu variants?
It's Ubuntu-based, true. I guess the Ubuntu poll option could have been more explicitly stating the variants. Anyway, I was referring to the distributions listed on http://releases.ubuntu.com/ i.e. Edubuntu, Kubuntu, Lubuntu, Mythbuntu, Ubuntu GNOME, UbuntuKylin, Ubuntu MATE, UbuntuStudio, Xubuntu.