I used to have a 900SS/SP and definately prefer the top-end power of the 4V twins over the 2V ones. But that's just personal preference. Even with the improvements over the years to the oil-cooled bikes I still don't think I could go back to one. They _are_ cheaper to maintain though and obviously less complicated to work on.
A testastretta Monster would just be pure sex IMO... hopefully I can snag a test ride on one this weekend.