Aside from traditional classics, I decided several years ago on my choices for the best-styled (timeless design) prewar and postwar AMERICAN cars.
Prewar: Gordon Buehrig's Cord 1936-37 810 and 812. I personally prefer the sedans over the convertibles, they were tastefully de-chromed and IMO were the template for the "running board-less" Cadillac 60 Specials.
Postwar: Although I love my 1964 Corvette Sting Ray, I have to give the prize to Raymond Loewy's 1963-64 Studebaker Avanti. Cool as a Corvette with room for four, if you update the wheels and tires each decade it still looks new.
Ironically both of these cars were introduced before the production kinks were worked out, leading to months of delays and hundreds of cancelled orders. I think a lot of people who placed deposits for Avantis gave up and bought the new Buick Riviera.