While the MATE desktop wasn't created by Canonical, I would say they perfected it with Ubuntu 10.04 (in its original GNOME 2.X form), and the community continues this tradition via Ubuntu MATE. The other distros provide MATE essentially unchanged from its initial appearance in mid-2011.
Ubuntu 10.10 was Canonical's last release to ship GNOME 2 as the default desktop. The final DE update was GNOME 2.32.1, which released in November 2010. GNOME 3.0 came out in April 2011.
The MATE desktop was forked from GNOME 2 over a 6-month period in 2011 by German "Perberos" Perugorria, an Argentine programmer who worked on Arch. Linux Mint provided assistance, and was the first distro to feature it later that year.
What I like about MATE is the history and heritage from GNOME 2.X's popularity, and how flexible it is. I can make the desktop environment look like Windows, MAC OS, Unity or any other combination without exceeding 1GB of RAM in daily use, any time I want.