I switched to Gnome because Marco has a regression in the way it handles multi-screen layout.
In the past, it was able to preserve window positions after adding or removing an external monitor.
Now, for instance if you configure a vertical layout (external screen on top of main monitor), all windows move to the top, e.g to the external monitor.
Open a few window on the bottom monitor, then remove the external one and this time windows would have a wrong offset, disappearing behind the panel.
So, every time, you have to rearrange all the windows. Worse, confidential windows may show up to the external monitor during a presentation.
Definitely a show stopper for professional use. What happened? Why did it loose the Metacity capabilities in this aspect (which only gnome-shell, among all DE, handles correctly).