Depends on which one strikes your fancy most.
Collectors pieces would be the early years (if you can get 'em and if
you have a ton of money) 53, 54, 55.
the 63 corvette C2 had a split rear window and is considered rare and
the Stingray C3's early years are the most collectible 68, 69, 70. Make
sure they have the 427 engine or a big block. Worth more.
The 80s 90's and the new ones are not collectibles yet.
Unless you want to steal the only remaining '83 from the corvette