I use Mint because I feel I have the access to the wide repositories that Ubuntu provides, including easy access to third-party software like Google Chrome, but I avoid a lot of problems I have with Ubuntu. Ubuntu tends to barf on my grub installation, Mint doesn't. Unity randomly crashes and stalls in both normal desktop usage and gaming (such as Team Fortress 2), while Mint doesn't include Unity. For some reason, Ubuntu will sometimes stall on boot when loading the Nvidia proprietary drivers for my Titan. Mint, for whatever reason, doesn't have this problem.

And, I'll be honest, as a long-time Debian and Ubuntu user, Unity saddens me. I really love Debian and Ubuntu, but I feel like Unity and some new decisions they're making is the elephant in the room for me. Progress is great, but it's hurting my desktop experience.