When slogans are messy then they are of no use. Generally difficult and complicated kinds of slogans are not liked by people. Most people don’t like to remember the slogans that are beyond their understanding.
It is best to go for slogans that are clear and easily understandable by all. They should be attractive in a way that they should speak of something that is inside many hearts and minds. That way they can get into the minds of most people that are targeted.