Last season Madrid was able to beat Man City with a quite astonishing score but that cannot be used as a reference for this season when they meet again, Madrid has improved its performance and Madrid's midfield and Madrid's attack line are also improving in my opinion. They almost have equal performance so the chances of both are still considered the same and it is also quite difficult to determine who will win this match in the end, Madrid has good experience in the UCL and has won many trophies but Man City wants to make a difference to the English team and try to beat Madrid in this big competition.
Slightly disagree with your opinion and I think last season Real Madrid didn't beat Manchester City with a big score but maybe what you mean is in the past meetings between these two clubs.
You say these two clubs have the same performance but I am very sure that Real Madrid will not be able to beat Manchester City anymore on the other hand if you really look deeper and compare the two clubs, Manchester City is much better which has a good performance in every line but look now after Benzema's departure Real Madrid can't have a strong attack line like before.
This season may be the next season that Real Madrid loses its chance to win the Champions League title.
You can see how last season these two clubs competed competitively while Real Madrid competed at home and was unable to get a big score when Manchester City very consistently defended against conceding big goals.
After that, the second leg, when Manchester City was the host of the match, responded with a bigger score and Real Madrid was unable to withstand every attack from Pep Guardiola's strategy.
From this historical experience, maybe you will understand better who the strongest candidate is between Manchester City and Real Madrid.