Bugner comfortabily, its unfair to compare him to Harrison, look beyond what you read and analyse their fightgames, Bugner was the truth compared to Audley he went 15 with Ali and was competitive with other very good heavyweights. Bugner gets a bad rap because of all the Cooper hoopla but the guy was lightyears ahead of Harrison and beats him on the cards in a cure for imsomnia.
Frazier 'made' Bugner fight or Joe would have been killed. Bugner never really wanted to be in there and Harrison is not in love with boxing either.
Realistically it has to be Bugner. Audley was never going to be more than British or European champion while Bugner on his day was class and in another era would have been a world champion. The only thing they have in common is their ability to play the pantomime villain, which in Bugner's case got him some nice paydays towards the end of his career.
Peak Bugner if he wanted to fight was a match for most heavies, probably even a title contender today.