My experience has been this. You go back to the 90's Suburban, the seats are awesome, it is like sitting on a cloud. Then came the next generation, same thing, seats are super comfortable, plush, and you snuggle on in. Come 2007, the seats are ok, a bit on the narrow side, but they are ok for comfortable, You drive it for 50,000 miles and it starts to take the shape of your butt and back, and becomes more and more comfortable as time goes on. Finally the newest seats are the least comfortable.
Every time I ride with my friend in his 04 Suburban it is so awesome, I could recline back and take a nap. My 07 sucks in comparison, but my imprint is becoming part of the vehicle at 70K miles of ownership.
The most comfortable seats seem to be those seats that have little to no adjustments. The old cars without lumbar and bolster support seem to be better sitting than anything newer.