#1. Sami Zayn

We'll admit that this is a decision we would be reluctant about. As a babyface, Sami Zayn had the perfect theme song - with some saying that it's the best babyface theme song. However, a year and a half into his run on the main roster, he turned heel and it's been over two years since he reverted - granted, he had a long injury spell as well.
But since it's been a while that he turned heel, perhaps his theme song doesn't suit him right now. He plays an obnoxious heel character who manages Shinsuke Nakamura and Cesaro and if the direction going forward is for him to remain a heel, then a change of theme song is a necessity.
However, should the direction see Nakamura and Cesaro turning on him, then it would make sense to keep the song. Either way, we don't see Zayn turning face just yet and perhaps the timing is key when pulling the trigger. Until then, he'll need a big change.