If I thought Leonard beat Hagler I would choose that one, but I can not. I would say the win that Bud pulled off was more significant, because he beat a fighter closer to his prime and also won me $400.
Leonard over Hagler. Mayweather and Bud were active fighters, Leonard only had 1 fight in the last 5 years. It'd be like Bud being retired ever since Covid hit with one gimmick fight against Barrios or whatever, and then coming back to beat Canelo now. Hagler also probably held the biggest genuine weight advantage here, with Floyd being naturally bigger than Pac and Bud not being not any more than 10 lbs lighter than Canelo naturally.
P4P based on their entire careers, I rank the beaten fighters as Pacquiao 1, Hagler 2 and Canelo a distant third. Mayweather was bigger than Pacquiao, whilst Crawford and SRL were the naturally lighter men in their respective fights. All 3 x beaten boxers were best their best, Pacquiao and Canelo moreso than Hagler, imo. Mayweather and Crawford's wins were clear, SRL's close and debatable. On balance, SRL has the best win of the 3. He was the smaller man, against an opponent closest to his prime and Hagler is significantly greater than Canelo.
Leonard beating Hagler Hagler was a complete fighter from top to bottom. Canelo has cherry picked and played weight games for ages. He lost both G fights IMO and that's after making G wait and wait. He then was completely outboxed by the one dimensional Bivol. The Canelo that showed up against Bud had become extremely predictable. Left hook to the body. Rt hand lead. That's it. Its all he does anymore. May vs Pac was many yrs too late in the making. Snooze fest.