In my own list this is how I rank em up;
1) Real Madrid
2) Manchester City
3) Bayern Munich
4) Inter Milan
5) Arsenal
6) Barcelona
I do think that Porto would be tough on Arsenal but they'll qualify ahead of them to the next round. I remember the last club that knocked them out of the Europa League Competition last season was Sporting Lisbon. As for Barcelona, they're one team with lot of inconsistency. Could they defeat Napoli? They could finally do that but they will not escape if they fail to sign up a good defensive midfielder. According to Cristiano Ronaldo, Manchester City are his number 1 option to win the Champions League Competition.
Actually seems possibilities with yours list teams potential become the Champion League winner for this season but I doubt when top teams from first until fourth number have to face early. Such as last season Champion League match drawing, Bayern Munich, Real Madrid and Manchester City have to face early and left Inter Milan with easy drawing match until success lead to final. However most dreaming Champion League final waiting for between Manchester City vs Real Madrid but both team have to face in semifinal match.
If drawing match scenario between Manchester City and Real Madrid have to face early I think both team get potential lead to final and my first number list favorite winner is Real Madrid.
If given a prediction of which four teams will play in the Champions League semi-finals, I think most people would have the same prediction. Manchester City and Real Madrid will surely have a place in everyone's predictions. Along with Real Madrid and Manchester City, Bayern Munich will be among the favorites in the Champions League this season. We can definitely consider these three teams as favorites for the Champions League this season. I think one or two of these three teams will qualify for the finals. I would confirm Real Madrid if they had a quality finisher in their squad but they don't have a quality finisher in their squad at the moment so they may lose their consistent performance in the big games. All things considered, Manchester City can be placed at the top of the list of favourites.