Duran, Leonard, and Hagler are three of the most versatile and complete fighters you'll ever see.
Duran and Leonard would be at the top. Duran mixed offense and defense as well as anyone that's fought. Very quick foot and hand speed, terrific combinations, heavy hands, counter punching, upper body movement. After establishing himself as possibly the greatest LW ever, he dominated Carlos Palomino at WW and beat an undefeated Sugar Ray Leonard there. The "Ray fought the wrong fight" thing is way overblown, Leonard was usually a flat-footed boxer who liked to circle, box in a relaxed manner, and open up with combinations. Duran was all over him, managing to be both ferocious and methodical at the same time.
Leonard's talent and ability was crazy too. He had good defense, pulling back from punches, staying at range and just moving his upper body to avoid shots. His left hook is one of the most underrated great punches in boxing history as far as I'm concerned. It was devastating. Leonard's power was no joke either, and he was an amazing finisher. Terrific hand speed, foot speed, footwork, stamina. As he showed against Duran in the rematch, and against Hagler, he could fight in a real fleet-footed manner as well.
Hagler would be third. Hagler's versatility was pretty amazing too. He could box both lefty and orthodox. He outboxed most opponents with his great jab, nice foot placement, and lateral movement, but came forward mauled Hearns. He was an excellent in-fighter, as Mugabi found out in the latter rounds of their fight. He usually had good parrying skills and head movement. I'll put Hagler below Leonard & Duran for prime-for-prime skills/talent because he lacked the speed of those two. He wasn't slow, but certainly not in their level with speed. Also, he had a pretty underdeveloped/underused straight left hand for a southpaw. Good left uppercut, but the straight left hand was kind of weak.
Hearns is the last of this list, but there's no shame in that at all. He didn't have the punch resistance of the other fighters, nor the in-fighting. But he could beat you in different ways. He could stalk and look to destroy you with the right cross, mixing in his devastating left hooks to the body, or box and move and use his range. Fast hands, very rangy. There's a reason why Hagler turned into a bull against Hearns. Because Tommy was so good at fighting from the outside and using his range and speed to outbox opponents. Tommy was beating Leonard on points through 13, and outboxed Benitez as well. He later outboxed an undefeated Virgil Hill.....at 175.
The fight with Hagler was about 4-5 yrs too late but even in that fight, Leonard wasn't given a chance. Yet he came out and showed that a great boxer beats a great brawler everytime.
Hagler-Hearns was a case where a great brawler (Hagler fought like one that night) beat a great boxer. While Tommy did exchange too much at first, he tried to box midway through the round at range, but Hagler cut him off. For the rest of the fight, Hearns tried to box and move, but Hagler kept getting to him.
Hagler was not normally a brawler, he just fought that way against Hearns because he had to, but he probably should've fought more like that against Leonard. He wasn't as aggressive as he should have been, but then again his style usually was more of a patient boxer than a swarming brawler.