Hmm, really tough to say. I pay most attention between 135lbs to 175lbs these days because of the tremendous talent floating around there.
In the current scene I can probably talk your ear off about any division above 115.... Not that I know nothing about the smallest weight classes, just those classes aren't real well publicized and most the fighters have long unpronounceable names. As far as history goes, its gonna be Heavyweight, Welterweight, and Middleweight... as those are where most of the big great fights have happened...
Yeah I'd agree with Heavyweight, Welterweight and Middleweight...these divisions have produced the greatest boxers in history in my opinion, part of the reason why I know more about these divisions than any other. Today though...I seem to follow all the weight classes between Featherweight and Super Middleweight.
Featherweight for me, because, obviously, Gamboa is in it:happy, plus, all the fighters are really willing to fight each other right now.