Don't have personal experience with either, but am a long time Harley rider, and tried really really hard to like the BMW GS enough to add one to my garage.
I like the relaxed nature of Harley V-Twin engines, with their low frequency vibrations (at least when rubber-mounted). I could not learn to live with the buzzy BMW boxer motor. Loved the motorcycle; hated the buzz. Tried 4 different BMWs, new to 10 years old, 0 miles to 50,000 miles. 1200 and 1150. They all had it. If you dislike buzzy motorcycles, the BMW boxer motor may not be your friend.