Here's a quick table showing some of the key differences in Ubuntu desktop environments.
At least the features I'm most interested in. With the negatives highlighted.
[table]
Feature,Gnome,Unity,Xfce,Cinnamon
Menu tied to Window (not at the top of the Screen like OS X),Yes,No,Yes,Yes
Default window close/max buttons,Right,Left,Right,Right
Default App Menu,Upper Left,Upper Left,Upper Left,Lower Left
Default App Dock,Left Hidden,Left,Bottom Hidden,None
Text Search for Apps,Yes,Yes,No,Yes
File Manager,Nautilus,Unity,Thunar,Nemo
File Manager Text Search/Filter,Search,Search,No,Search
File Manager View Change Buttons,Yes,Yes,No,Yes
Nice Desktop Config,Yes,Yes,,Yes
Nice Wallpaper Config,No - Use Wallch,Yes,,No - Use Wallch
[/table]
I really like the Unity file manager, it's very quick and has all the basic features. I also like the Gnome file manager although it's not as responsive as Unity. Don't really care for the Xfce file manager.
There are other good review of Ubuntu desktops environments here and here.
I prefer Gnome or Cinnamon and use Wallch as a wallpaper changer. I also like focus follows mouse and run dconf Editor to set auto-raise, auto-raise-delay and focus-mode. For Cinnamon this is found in dconf Editor at org.cinnamon.desktop.wm.preferences and for Gnome at org.gnome.desktop.wm.preferences.