The Rainier has proven to be comfortable and it performs well. The air suspension makes for a comfortable ride and the interior is very quiet. My city mpg has been about 14, and on a recent 2800 mile trip my highway mileage was just under 20 mpg with 4 passengers and a full load. The only problem I have had with the vehicle was a molding on the rear hatch that came loose.
Driver seat comfort level is terrific, the vehicle has lots of get up and go. Interior is very quiet. I have found the OnStar system to be very useful.
Cup holders in the front seat are poorly designed. One is essentially useless which leaves one for the front seat passengers.