Both are important at their places so you need to tell your interviewer that how you balance both the things. You need to focus on a strategy that makes it clear that you are willing to prioritize what is most important for that given situation in order to meet company objectives.

I think that the key is a balance between the two, with efficiency being the most important. You could have an extremely creative piece, but if the message of the piece is not clear then it is not efficient and a waste of resources.