Well, owning a 6.7L I am a bit biased. I love the factory exhaust brake and 6 speed auto. But for a growing family that Mega Cab is really hard to beat. Quad cabs are a cross between an extended and crew cab. Not as much room as the genuine crews, but bigger than the extended cabs. The down side of the Mega cab is payload. It is generally less than comparable quad cabs. Also the short bed is a draw back for lots of people. Next is rear axle ratio? If the two trucks are equal in all aspects I would opt for the mega cab and add a slider hitch and go.