I have been using Ubuntu for the past year or two and I am not sure which desktop environment or flavor to use when I do this in a few days.
I personally like KDE better however I have had issues with it in the past for example anacron starting over and over and over again and the only way for me to stop this from happening was to make a startup script that has pkill anacron about 30 times in it. This is the kind of thing I want to avoid in the future.
I started getting used to Unity however I really don't like it that much. From the screenshots it looks like the MATE desktop is pretty much a Gnome2 clone? If this is correct then I would probably prefer that although I want Ubuntu and not Linux Mint. (installing it is easy but I am worried about bugs)
I just want something that is easy to use and customize as well as quick. KDE would be great even if its not quite as fast but the above example is just one of the many issues I had so far and I would like to avoid them. Also when I run KDE on my laptop it gets really hot and then freezes but this doesn't happen with other desktops and makes no sense whatsoever to me.