I thought Marvelous Marvin was definitely one of the toughest guys out there. I liked Sugar Ray by what he did in the Olympics, but there were several heros on the 76 team like the Spinks brothers and Howard Davis. We use to call Leon Spinks the grill because of his missing dental work, but he, too, was a bull in the ring: just ask Cassius Marcellus.
But Leonard was an excellent boxer, but so was Hagler as well as being a brute; and although history says differently, Hagler won the matchup. As YL noted, Marvin was the Champ and, at the time, challengers had to bring the fight to the Champ if they want to win; Sugar Ray did not do that but the victory was given to him. A complete traversty!
Marine brought up Little Red Lopez. Another star boxer who had pretty well been spent by the time the 76 team started their run at championships. He could take a beating and get up to win, but he was done by 1980.
It was a great time for boxing but it was losing its appeal when Hagler revived the sport by winning and holding his title for so long. Knocking out Hearnes (who was suppose to grow into a light heavyweight), was his peak as well as the near end of boxing's heyday, it has not been the same since.