Bah, I misunderstood gnome-flashback. It is not a full DE but rather a session for gnome3, which is probably why the homepage says:
GNOME Flashback is a session for GNOME 3 which was initially called “GNOME Fallback”, and shipped as a stand-alone session in Debian and Ubuntu.
So the 30% gnome3 number includes all the gnome-flashback users. Test by installing gnome-session-flashback gdm3. I thought it would come with all the baggage in gnome3 but it feels rather light. Desktop is very familiar as expected.
My personal picks are:
kde framework: kde5 (need to test - wait until 5.8 as HulaHoop suggests) or lxde (need to test)
gtk framework: gnome-flashback
I like xfce4 personally but I have my doubts about whether it would make a good newbie DE. A trivial example: if you right click a .desktop icon, the first menu choice is “Execute”. Only geeks say execute - the rest of the world says, “Run program” or “Launch application”. How many newbs even know what an executable is?
another example: to edit the applications menu,
- gnome-flashback: right-click applications menu
- xfce4: I couldn’t figure it out last time so I had to go look it up. I remember I edited some config files. I’ve since forgotten how to do it and so had to go look it up again. howto:customize-menu [Xfce Wiki].
Apparently we can install menu editors…