My vote for Moto-Guzzi. Older ones are easy to maintain, realtively cheap to find, you wont see yourself coming and going. I had an 81 LeMans 850 and loved it. My Brother rides a 79 SP1000 with over 90k on the stock motor. Sounds great, rides great, shaft drive. Check out
www.harpersmotoguzzi.com for all the info you will ever need.
This is exactly what my old bike looked like.