The thing is, Blizzard can just toss up an ingame survey to figure that out or look at one of the existing surveys.
Ex:
King’s Row was the favorite of 32% of the game with 19k responses.
What people like and dislike on maps isn’t necessarily the same. For example, I hate 2CP and what I hate about 2CP is what other people like about it. Changing 2CP to make me happier would possibly frustrate the people that like it (and people do like it).