I can honestly say that I have distro hopped just about every major (and quite a number of minor) linux distributions out there. Consequently, I can say that I have landed with Ubuntu Mate not out of ignorance, but out of a deep experience with and understanding of all of the different strengths and weaknesses of all of these variants of Linux.
I have no particular penchant for Ubuntu per-se. It's the Mate desktop that does it for me. However, out of all of the various Linux distros that ship with the Mate desktop, Ubuntu is by far and away the one that has integrated the mate desktop to the fullest extent. This is the reason I use it over, say, Mint Mate (which would be my second choice of distro shipping with Mate). The Mint version of Mate is just a little bit too buggy compared to Ubuntu Mate.
Basically, Ubuntu Mate has it all. It's rock solid, easy to use, looks great and is extremely customisable. It just ticks all of my boxes.