I would buy the F800GS again because it fits my long body much better and I wanted the more offroad oriented bike. The XC just does not fit me off road. As a mostly on-road bike it would probably have been the better choice for me but that's not what I wanted.
Only you can answer the question what works for you. Ride them both, think about what you expect from the bike and then buy what suits you best.
"Rumors of my assimilation are greatly exaggerated." (Capt. Picard)