Duramax w/ Allison Trans is the way to go. I regularly pull a 13.5K fifth wheel and sometimes forget it is back there. Rides better than my SUV, gets better fuel economy (gotta love a diesel) and has all the same creature comforts. I would definitely buy again, although I'm thinking I won't have to.
Diesel - fuel efficiency and cost can't be beat. Leather and Bose surround aren't bad either.