Ali v Holmes (heavyweight), 15 rounds. I assume you mean prime vs prime. In my opinion Ali is faster and Holmes has better fundamenatals. This is a tough one to decide. I think Ali's speed is foing to give him the edge. Ali 9 Holmes 6 Hagler v Hopkins (middleweight), 12 rounds. Hopkins will pick his spots and Hagler will go to (as his famous hat said) war. Hagler's work rate will cary the day in the end. There will be times that Hopkins will apear to be the better boxer but not enough times to win him enough rounds to win the fight Hagler 7 Hopkins 5 Duran v Whitaker (lightweight), 12 rounds. There is no chance that Duran can out box Whitaker and Duran would know this. Duran would take on the roll of puncher to Whitaker's boxer. Both re most comfortable in these rolls. Duran is an underrated boxer but Whitaker is just as much an underrated puncher at 135. He also has a high work rate. In short Whitaker makes Duran look like a mere mortal. Whitaker 9 Duran 3.
Muhammad Ali wins in a nip & tuck fight for the first 10 rounds but starts taking over from rounds 10 onwards and wins a unaimous decision Hagler wins close decision over Hopkins who gives Hagler fits during most of the fight but Hagler makes the necessery adjustments and wins deserved decsion. I love Roberto Duran but I don't know if he could beat Whitaker who is in my opinion a top 3 all time technican and has unbelievable ring craft , I'd love to say Duran but I have to pick Whitaker based on when Duran fought a fighter as elusive as Whitaker in the form of Benitez he could not adjust to that style of fighter {i know it was at 154 Lbs but still} so my pick is Whitaker by 12 round decision.
Ali prime versus prime is better than Holmes in almost every department, except possibly for the jab. Hagler in a close contest in which Hopkins tries all the dirty tricks in the book. Whitaker can't be stopped by Duran. Sweet Pea by UD