MATE with GTK 3 would be nice.
But it would be a lot of code duplication of doing lots of stuff upstreams in GNOME 3. The code bases diverse so much that they probably cant backport anymore.
But I think GNOME 3 with GNOME Fallback Session is pretty good, its like a classic GNOME 2 desktop almost. However Cheese, gcalc and some apps get retarded menus.
Unfortunately I heard they might discontinue GNOME Fallback Session.