I voted Ubuntu, but only because with mint I've had a few issues getting things running right. Also, ubuntu worked straight out of the box for me, whereas with mint I had to spend time configuring a bunch of drivers.
I think that's just because I made a few errors on my part with mint. YMMV.
All in all I like both- they're extremely similar and I use a billion and one desktop environments anyways, and the two I use the most are Gnome 3 and LXDE- I don't give two turds about Mate, Cinnamon or Unity.