I`m going with Ali but one way or another he would have done better than he did in the `71 clash because he was lighter and faster.
66-67 Ali was superior over '71 Frazier. Major problem is Ali pre-fight, might actually believe he is "superior", pull a "Chuvalo" type inside fight, and by the 10th round realize that Fraizier is nothing to fool around with, and end up losing a UD or SD.
Ali, really close decision. Ali was much quicker on his feet then, stamina was excellent, but Joe could find Ali in every one of their fights. That is what Joe did well. Also depends what year the fight took place, in 67 Ali gets the close decision but in 71 Frazier would get the close decision. Popularity contest.
Probably no news that I go for Ali but also think it's interesting to speculate how things would have worked out between them if Ali never was exiled. Joe actually had established himself as the top contender by then, so they could have met as early as late 1967. I think a meet bewteen them would have taken place in 1968 at the latest. Things would really be in Ali's favor in that case since Frazier had yet to reach his peak by this point, but maybe some interest still could be drummed up in the fight, not least by Frazier's insistence on calling Ali "Clay". That he, unlike Ali, managed to stop Chuvalo would also be used for the promotion and perhaps provide Ali with something to prove. Even though I think Ali wins quite comfortably against a less mature Frazier, Frazier would probably test him more than any other title challenger and a rematch would probably happen down the road. Say the rematch happens some time 1970-71. Frazier will have reached his peak by this point while Ali possibly could be a bit jaded. I don't think age would be a big factor for him, but rather having been champ for a long time and not really putting in the effort anymore. So an upset could be on the cards here, or at least a close and hard fought fight, followed by a rubber that a fully motivated Ali wins.
