My vote would be for one of the VCA one-offs. The raffle cars are unique in that they have no doubles at all.
Collectable Snakes would be :
Not necessarily in order
GT-2's
1992's
Final Editions
Raffle Vipers
ABS cars
96-99 Blue/White GTS's
97 RT-10 ,Blue /White
Cars built with a one year color, or low production color stats
( example Steel Gray, Silver, Graphite )
Any Viper ---- heck there may only be around 12,000 in the country anyway, and there are 36,000 Vettes built in one year.