Oh my, now that's a really hard question! And one I've though about often with no solid conclusion.
BMWs are unsophisticated, overweight and plainly not reliable. But they will carry you in reasonable comfort, they are fixable and rarely actually stop dead in their tracks.
Even 5 years later and with a new motor in mine, it still feels like "home" when I set off on even the shortest of trips.
Sean
ps In my opionion, the absolute PITA on these bikes is stripping out the studs when torquing down the cylinder heads. At risk of teaching anyone to suck eggs, do not trust any mechanic with this task.