I agree with Les on the Ultimate seats. Last month I rode over 6,000 miles on my 1100 and I never had a butt ache. The backrest is part of that but it's been great. I don't have any personal experience with the Mustang seats but I've heard good things about them too.
2002 V-Star 1100
You don't stop riding when you get old, you get old when you stop riding
2004 BMW K1200GT
1995 BMW 1100 LT
1970 Honda 500/4
1969 Kawasaki 500HD - 3 cylinder rocket
1968 Yamaha 250