Competition in the Champions League is not that simple, even though we think some teams are favorites we don't know what happens to them. Maybe many here look at their performances, including me, but when on the pitch other factors besides the game are also very influential for the results that will be obtained by the competing teams. Luck, mentality are two things that will be their shadows in every match, even though they may meet weaker teams.
Manchester City are the favorites, Real Madrid and Bayern Munich are on my favorites list as well, not to mention Real Madrid's main rivals in La Liga, Barcelona.
Talking about luck and mentality, of course these are two different things. Luck is possible for all teams and there are many unexpected things throughout the competition. But in terms of mentality, I think it still belongs to Real Madrid. We know that the king of the Champions League often makes the impossible come true and we have certainly seen it since then when Real Madrid were able to win the UCL title against Atletico in 2014. Since then their mentality has continued to grow and the results are up to now they can still surprise people with results that should not happen. This mentality continues to inherit the current generation of Real Madrid and it will be an important strength that other teams rarely have.
Apart from all that, Manchester City is still the favorite because they have better depth than all the teams. Bayern Munich and Real Madrid will always try to win their title back and for Barcelona they are the longest team after last winning this competition in 2015 and of course they will also be aiming for the same thing.