I've read about the 1100's problems with its gearbox and final drive, and I prefer the beak of the 1150.
I want to go to Russia on it next year and want something that can cope with it all without the bearings going on me, and something that will still be reliable when I return to hit the M1
From my 11yrs with 1150s and in that time and before knowing about 1100s, I'd say the 1150 are more prone to gearbox and final drive problems not the 1100s, but never experience any problems with either myself
Don't think there's a straight forward answer to 'better' for any bike, it depends on what you're going to do with it, how tall you are and how competent a rider you are ...
ie. if you're tall and good, the ADV may be best allround, but then my ADV is not standard (for a good reason!)
The GSA is higher, I'm 5'11 and the GS is high enough and frankly I'm not likely to use it's suspension travel or ground clearance touring and wild camping without the need to full off road tyres against tyres like Distazias or Tourance.
Same way I'm unlikely to use the extra low gearing of the GSA, the big tank is nice but a liability off road and I doubt I'm ever so far from a petrol station to make the weight sacrifice worth it.
I don't like the GSA seat the bonus of the GS tool kit tray is spot on and I can remove the rear seat and carry stuff on the flat bed.