1) When was the last time Ali was the best heavyweight in the world? I would say the fight with Foreman was the last time Ali was definitely the best heavyweight in the world, having recently beaten Norton and Frazier as well. 2) When was Ali at his best in the 70's? I think this is debatable. You have to weigh the fact that he needed time to get rid of the ring rust from being out of boxing for over 3 years with the fact that passage of time meant that he was going to decline physically. I think the most likely times are the first fight with Frazier, the second fight with Norton or the Foreman fight.
The Foreman fight for both questions although one could say how could he be called the best HW in the world when he didn't have the beating of Norton. Being labeled as one of the best HW's was probably more fitting IMO.
I think Ali beat Norton the second time round. I'm probably in a minority in believing that Ali won their third fight but I think that was down to Norton boxing too cautiously especially in the 15th round. There was no need for caution. Ali was never going to stop him in 1976 and if Norton had been more courageous he would have got the decision.
Thrilla in Manilla was the last time he was the best, though I can hear an argument for up to the Shavers fight Frazier vs Ali 1 to Frazier vs Ali 2 was his peak in the 70s
I'm not sure how Ali would have coped with Foreman if the fight in Manila had been with him but then again Foreman had disappeared from view at that time. I think that by the time of the third Norton fight he was no longer the best in the world. Ali was in shape for this fight but Norton still showed he was the more effective of the two but threw it away through being overly cautious.
1) Ali was last "the best" going in to the Jimmy Young fight. He'd beaten Frazier, Foreman had just gone life and death with Lyle, and there were still some questions about Norton. Young, and Norton later that year, showed that Ali was ready to be taken. 2) Ali had three 70's peaks - Quarry II, Norton II, and Foreman.
1. Manilla was probably the last time Ali was the best HW in the world. 2. His 70's peak was probably something like 1972-1974. Or in more specific terms Quarry II - Frazier II. He actually seemed to have lost quite a bit of foot speed between the Frazier rematch and Zaire.
