I'm a dinosaur. I've been using the same fvwm2 configuration since 1996. I've tried other window managers, with varying levels of sincerity, but I drift back to comfortable old fvwm2 with no window decorations sooner or later. (I got along really well with Blackbox, but it was easier to switch back than to hack the code to cycle forward and back through a stack of windows with RaiseLower, a feature I like.)
I've also tried hard to get along with the default desktop on successive versions of Ubuntu (both GNOME and Unity), but a day or two is all I can stand. But there are some things about the Ubuntu interface that I don't want to give up or reinvent, especially on my laptop (the keyring, some indicator applets, nm-applet, the screensaver, etc.). Being an adaptible dinosaur, I now run fvwm2 as my GNOME window manager.
Thanks to this detailed explanation by dedicated xmonad users, changing "xmonad" to "fvwm2" in a few places was all the hard work I needed to do. I had an ~/.xsession file that ran a few startup commands already, so I put the following into /usr/share/xsessions/xsession.desktop to add an "xsession" option in the session drop-down at the login screen:
[Desktop Entry] Name=xsession Exec=/etc/X11/Xsession
Then I created /usr/share/gnome-session/sessions/fvwm.session with the following contents:
[GNOME Session] Name=fvwm2+GNOME RequiredComponents=gnome-settings-daemon; RequiredProviders=windowmanager; DefaultProvider-windowmanager=fvwm
That was enough to make "gnome-session --session=fvwm" work, and that's what the last line of my .xsession runs. The other bit worth mentioning is stalonetray, which provides a home to nm-applet and friends.