It's been said
By two different posts, so far. Mine will make three. I have both a Buell Lightning Long, and a BMW Rockster (think sporty r1150r), and 100% if I HAD to choose one bike, BMW.
Three people have now told you what you should already suspect. The BMW is the ride that you'll always use, and will always do you right.
The Buell is fun, fast, and great, IN CERTAIN SITUATIONS. Long distance and with a passenger are NOT those times.
What was said about maintenance is correct. BOTH are really reliable, thought the Buell has left me stranded WAY far from home, while the BMW has NEVER come close to that. The BMW has 50,000 amazing miles on it from me, the Buell has 17,000miles and I LOVE to commute to work on it. I'm 5'10 and both bikes fit me well, though the wife is fond of the Buell, she will ONLY pick the BMW for any trip, short or long. It is SO much more comfortable, and all my friends with the GS sing the same tune about their girlfriends, and wives. Though I'm the only one with the Buell as the speed bike. If you test ride them, bring your significant other, or just assume that YOU will never want or ask anyone to be on there with you.
2004 BMW Rockster