Having owned 3 C3's over the years('69, 73 & 79), the '79 was my least favorite, probably because of the seven Corvettes I've owned since '77, it was the 'only' automatic, LOL !
With regards to your comment on 68-70, the 68 would be the least desirable for it had body panel fitment issues galore that if not repaired correctly would be a large expense. But if one is seeking a superb 'driver' then for the $$ spent a mid seventies bought on the cheap(as 'Dude' pointed out) and modded out from there would be the way to go IMO. Keep in mind on both the C2&3 that the frame and 'bird cage' integrity is critical.