They all have their good and bad points. It also depends on what you plan on doing with them.
66-77 I honestly don't know much about these classics other then you can find some parts being made for them.
78-79 Good classic design with lots of re-manufactured & aftermarket parts available. The solid front axle makes this one a good year for off road. Very strong. By looking at what is available for parts this has to be the most popular era.
80-86 My personal favorite due to its looks but it does have a few drawbacks in my opinion. Emissions systems seem to get worse and worse as they went along. The carb on my 85 was a nightmare for me to work with. Add to that the fact that parts for these years are considerably harder to come across outside of places like Napa ect... It also does not have a solid axle. They went with a different kind of suspension (Twin Traction Beam) that isn't as strong but offered better road handling.
87-96 More rounded body design. EFI became standard in these years. Still no solid axle though. As for a daily driver on the road its probably one of the better ones due to emissions, highway drive ability, and gas mileage.
These are just my opinions.
