Pound for Pound, I'd put them

1. Duran
2. Hagler
3. Leonard
4. Hearns

Couldn't complain too much about someone ranking Leonard over Hagler, but for me, Marv's body of work earns it. (1/2)

11 years without a loss, 12 successful title defenses (and could have easily been more, but he didn't get a title shot until he was way overdue). Only 1 guy ever clearly beat him, and he avenged that loss with two stoppage wins.