I'm a fan of the heavyweights (not the current crop though), the middleweights closely follow and the welterweights are just below that.
160 has been my favorite for years. However, with guys like Darchinyan, Cermeno, Agbeko, Donaire, and others on the scene I've started to pay a lot of attention to the little guys.
I chose heavyweight purely because of the great fights over the years and Muhammad Ali fights getting me into boxing. But the middleweights with the marvelous one and the welters are a close joint second. At the moment most peoples favourite class will be welter and it would seem that is the weightclass which consistently produces the best talent. On another not lightheavyweight has never really appealed to me. Its probably because big light heavy's are always looking north i guess.
Lightweight Middleweight Welterweight Heavyweight Lightheavyweight Don't know why but the little guys somehow don't interest me much - with some exceptions of course.
Welterweight. I used to like Middle but it's terrible right now, much like Heavy. I'm not all that fussed for the small guys, below Bantam.