The best is obviously Pep Guardiola. He must be. After all this is City's biggest forum and I'm a bitter Berti with my biased blue tinted specs on. Oh hang on, he's only been here 4 seasons. Great manager, our greatest and most successful. We're witnessing fantastic football, the most beautiful football I've ever seen. Many records broken in the EPL and a clean domestic sweep last season. Only time will tell if he is to supercede the trophy haul of a certain Scotsman though...
The best domestic manager in the history of football is Fergie IMHO.
He wrestled the trophies from the grasp of Glasgow powerhouses Celtic and Rangers, winning three league titles, four Scottish Cups, one Scottish League Cup, the Cup Winners Cup and UEFA Super Cup. All this in 8 seasons whilst managing Aberdeen.
Then he went to the rags in 86 and was unsuccessful till '90. Perceived as a failure, his managerial epitaph was(allegedly) already typed out by the press who had inside info on him getting 'sacked in the morning'. Up popped Mark bastard Robins with a very late looping header at Forest, 3rd round FA cup game in '90. And the rest is 'istry as they say, Robins definitely saved Fergie's bacon that day, and they went on to win the cup. And us blues old enough to remember that goal, know how much pain and suffering we've endured whilst he was in charge at the swamp: (
His trophy haul speaks for itself. The squads he's evolved and the youth players that have come through the ranks to have very successful careers under his tenure is there in the football history books. Whether you agree he's the best or not is your opinion. My opinion is as above.