In my opinion, the biggest favorites are City and Real Madrid, although Bayer Munich is a team that loves the championship, I can say that they have not shown any weakness at the moment. As the eliminations approach, the pieces will fall into place.
I think one of the three teams you've mentioned above (City, Real Madrid and Bayern Mumich) will be champions, of course City are the defending champions (having won the CL for the first time last season), and they'll want to defend their title. The thing i love most about City is their lack of complacency, they always want success every season, notwithstanding whatsoever they won the previous season.
City beat Bayern (in the QF) and Real Madrid (in the SF) on their way to the trophy last season, and if they meet either team in this knockout stage, it would be pretty tough and there would be a sense of revenge. It would be interesting to see how things pan out.