If you want something that can "comfortably" fit 4 people you need a Crown Vic or something like that.
My thunderbird has a bigger, nicer rear seat than a Mustang, but it still wouldn't really seat four adults "comfortably," plus nobody over about 5'4" would ever be sitting behind me
i sure like my mustang, rides comfy on the hwy, gets decent mileage and is pretty friggin quick, and my friend didnt complain at all riding in the back seat 4 hours, and he's 6' & 200 something lbs