1968-1971 to me are the important years.
For a vast majorioty of people, those are the key years and you will pay plenty to get into the cool club with those models if you don't already have one.
I can't say I have a favorite. In general I'd say 28-36, 55-58, and 63-80. I can find things I like about almost any model in any of those years, even the smogger, decal cars. Back in the 80s I tended to have 68-71 models cuz they were cheap. As the prices got silly on them I've tended to pick stuff up on the fringe instead. My current crop consists of a 67, a 73, two 74s, and an 80. I used to have a 58. Never had any depression era stuff, but I'd sure like too.