I've got both
I spent a few hours today riding my 1150 and f800 GS's ... Needed to run them before it gets really wet here. For how you ride I'd have to say the F800GS would be more fun, but as others have noted I'd be hard pressed to leave the R1150GS in the garage if I were riding to the Yukon this summer. Trips from LA through out the Southwest would be a blast on the F8 and knowing I could take off down any road I come across is just sweet. That's something I now hesitate to do on the 1150 mostly because of my last spill on the Dempster Highway in '05. I spent 30 minutes waiting for someone to help me pick the GS up and I really don't want to chance injury and that feeling again. I am a solitary rider by nature and I did break a rib in that Dempster crash, so take that as a FWIW.
Bottom line, from the three months I've had the F800 is it's become my favorite bike and I just might have to sell the 1150. I'll let you know but it's a definite thumbs up for the F8GS over the R1150GS from me.
What the hell do I know?!?