Just Chevy alone, I'd have to say 1966. Impala, Nova, Chevelle, Corvette, heck...even the pickups were good looking. As far as a year across the board for all manufactures, I'd have to say 1959. I feel like that was the year that everyone took it as far as they could. Just like 1970 was the pinnacle and grand finale of the muscle car era, I feel that 1959 was the grand finale of no-holds-barred styling.