#2 Charlotte Flair
Charlotte Flair arguably enjoyed her best days in WWE as a heel as far as her character is concerned. Just like her father The Nature Boy Ric Flair, although she is likeable as a babyface, it seems she fits the role of a heel far better.
Turning Charlotte heel and having her team up with the likes of Lana or Absolution could help Charlotte, but also give her partners legitimacy and propel them to the next level. This is an option the WWE could explore, but Charlotte is more than capable of going solo and being the champion every woman on the SmackDown roster has to try to beat.
Charlotte has said in an interview with the LA Times that she prefers to play the part of a heel. The Evil Queen character certainly seemed to be a role that Ms Flair was more comfortable playing. The Nature Girl is far more suited to playing the cocky, 'better-than-you' heel, certainly in terms of her mic work.
It can be refreshing for a character to spend some time a face for a while, but it seems Charlotte's long-term future should lie as a heel.