Impala seems to be the top of the heap (with the SS being the most popular). Few go for the Kingston estate wagon though I like long roofs), or the cheaper Biscayne or Bel Air models. Everyone wants a two door sport coupe body with the four door having to be a hard top as well to be anything but a parts car. Most don't recognize that a sedan body is lighter and stronger if you want to race it (or to build a sleeper, like I enjoy doing).
People forget that before 1965 the full size and the Corvette were the only V8 powered cars from Chevrolet. Once the Chevelle was introduced in 1965 with a 396 BBC as an option the idea of a hot Chevy being anything other than a two door sedan biscuit with a big block under the hood never occurred to anyone. Once the Camaro was added to the mix in 1967 people only thought of the full size as anything other than a cruiser for the family (why there were more four door cars sold than two doors; that had little resale value as a used car).
I rarely hear about the Caprice, even though when they were new the Caprice was much more popular (hence the higher price). Everyone that my mother met with her 1968 Caprice four door sports coupe thought she was driving a Cadillac. Because the caprice is unique amongst Chevy's (having a different roof line as well as interior trim) I doubt if you could justify carrying parts for it until it becomes much more popular.