For me I can't pick just one because the three I have chosen were all of a different time, but all to me are legends.
1: Joe Mercer/Malcolm Allison. I put these as a team because both admitted they just complimented each other perfectly and when they split that proved to be the case. As a kid they were my absolute heroes and I hung onto every word and believed with them at the helm anything was possible. Until recent events they managed the best players and most successful period in our history and played great football too.
2: Roberto Mancini. He came into the club when the euphoria of the takeover was waning. Although we were obviously better than we were, which wasn't difficult, we weren't ripping up any trees. He tightened things up, gave us a meaner edge and a winning mentality. He connected with the fan's and I don't give a shit what anyone says or who he fell out with he got us, he really did. He rattled Ferguson like no other manager ever had and played a blinder when it looked like we had blown the title. He promised to rip down that fucking banner and did it and moved the mentality of the club to a whole new level. Don't forget we had won nothing for 35 years and no title for 44 and he put that to bed. A legend.
3: Pep. An absolute football genius who has the team playing the best football I have seen in 50 years of following City. We are privileged to have him and watch the football on the pitch he creates in his head. Long may it continue.
No sane City fan could argue against anything you have said here.