This thread is about car design in game so please don't post requests or something. Personally I don't like Barstow. It's too "flat" for being a muscle car. Front and rear looks good but from side it's looks like box. For me Gavril Bandit from RoR have best looking body. Lack of details but that line is neat. Another car with great design is Miramar. For me it's best car in game. Also Moonhawk isn't bad. Rest are just regular, nice looking cars.
I personally don't care for the miramar. The body's proportions are off, with the trunk and hood being relatively small when compared to the massive, boxy passenger compartment. My personal favorites would probably have to be the Moonhawk and the pessimas. They are the perfect stereotype of their styles, and just work in game.
Miramar have good proportions for me. This is how some cars from 60s looked in Europe and Japan. Probably illusion of massive central body are big glasses on sides.