Compatibility: XFCE and gnome are both good to use and good to know and good to use and what makes them both the winner in this group is becuase both are good with user interface and user experience and to say that one is better then the other in this category is a lie becuase both have some tremendous capabilities in the right hands and with the right systems and perimeters in place
Scalability: Gnome takes this category by a long shot with its integration on multiple interfaces and its ability to launch on almost any platform its way more scalable then XFCE and will continue to be the best in this category hands down
Mobility: Both are good in this category and I would say that becuase both are mobile friendly and both can be operated on a mobile device but not all mobile devices due to recent changes and updates
Freaking Tweaking: XFCE wins by a long haul its ability to tweak the code makes this program and the ability to do virtually anything. the user has the sky and some to do what he wants in terms of options and user feeds and optimizing this useful
Simplicity: XFCE is the user base that is the most simple but also the most complex to use and what it lacks in looks gnome makes up but its ok it still wins in this category
User Friendly: Both win in this category because they are both good programs to learn and to master depending on the amount of work you plan to do and the scale of it.
Overview both XFCE and Gnome have capabilities its all up to you to choose the right platform that your most comfortable with and feel more like home with.