I think there is no point in waiting to replace Mourinho. We should do this now, when it is still possible to salvage the season.
Regarding the next manager I would like, my option is Laurent Blanc. Looking at the other mentioned candidates that we realistically have a chance to get, I really do not find anyone else whose managed teams so far had an adventurous, attractive game like we used to have under the guidance of Sir Alex.
Pochettino? I believe he is a good manager, great fit for Tottenham but not for United. He may be able to deliver top 4 performances, but I don't think he can bring us to that level of title challengers.
Allegri? Ancelotti? Conte? Italian managers, can maybe bring trophies but we would not play an attacking game and, in my opinion, they won't last more than 2-3 seasons.
Zidane? He may be a great manager, I don't know. He inherited the team at Real Madrid, he did not build it so I do not know if he has he capability of doing this.
We must be realistic: Manchester City has a great team and a great manager right now, they play the best football and they are the team to beat and will be in the following seasons (in England at least). I believe, with the history we have, we also deserve to have those things they have.
Laurent Blanc is an excellent manager whose performances speak for themselves.
He took a mediocre Bordeaux team, made a lot of transfers (but not expensive ones) and managed to win the French league with them surpassing Lyon (who had a great team and had won the league in the previous 7 years) and next year he reached the QF of the Champions League with Bordeaux. But, most importantly, he made them play an attractive attacking game similar to what we used to play under sir Alex (you can check youtube videos about that Bordeaux team from 2007-2010).
I won't speak too much about his time at PSG, but you can see that he also won a lot with them and (very important) he managed all the player's egos very well.
Blanc has one of the best managerial stats from all the names in the poll list, he is a proven winner and, most importantly, his teams win in style. The best thing is that he is currently unemployed (he had lots of offers and turned them down because he is looking for very serious projects) and is familiar with our club and the pressure that the job instills.