The 2 valve air cooled are more reliable IMHO and they cost less to do any valve adjustments if you dont do them yourself. If what you have is plenty of power, then why sacrifice more comfort, more reliablity, and less money to maintain? If you want more power, then it is a different story. If you want the comfort AND the reliability, then the 1000DS would be a great choice. If you want alot more power, then consider the superbikes.

All the bikes are great bikes, but it depends what you like and what you intend to use it for. (Track days, weekend twisties, commute, etc.)