I don't think Real Madrid are far superior to Chelsea this season. Real Madrid's defense is not good, their midfield is not as good as a few seasons ago and they only rely on Benzema as a goalscorer. You will probably know that there will be a tight guard for Benzema in that match if he is really available, and that man-marking strategy will get Real Madrid in trouble.
You might as well put Real Madrid ahead. But in the first leg, I want to keep Chelsea ahead. This is Chelsea's home match. Last season we saw Chelsea easily win 2-0 at home against Real Madrid. My guess is that this season we will see similar results in the first leg. However, Chelsea's performance at the Santiago Bernabeu will depend on which team qualifies for the next round. Real Madrid is always strong in Bernabeu.