If youre not sure, dont buy it. Personally I would get an older model such as the early 70s, before the they were required to have a cat(which was in 1975). The older years are worth more and built a little better. The engines also were built better and had better compression and power. If youre gonna guzzle gas you might as well get some power out of it, and you wont with the later models.
This is all coming from the purely muscle car standpoint though.