#3 Apollo
One of the most gifted athletes in WWE, Apollo's career has failed to take off majorly because he was called to the main roster very soon, without having much experience in NXT.
Many of the NXT stars have failed to make an impact on the main roster and are used as enhancement talents but Apollo has much more capability than to be wasted as a jobber.
The main problem with Apollo seems to be his extremely generic character, so a stint back in NXT would help him find a more entertaining side to him which will help him connect with the audience more.