#1 EC3
EC3 had a pretty forgettable run in NXT as Derrick Bateman, during the shows original incarnation. However, he parted ways with WWE and joined Impact Wrestling, where he became the face of the brand. In Impact, EC3 was a two time World Heavyweight Champion and defeated every top star that came his way.
EC3 returned to WWE and NXT in 2018 but had a surprisingly underwhelming run. Although it wasn't great, he still appeared regularly and got victories over the like of Adam Cole. EC3 was brought to the main roster with a big push in mind and even defeated Dean Ambrose in his first match on RAW. However, things went downhill very quickly and he has only made sporadic appearances over the past few months.
These days, the only time you will see EC3 on WWE TV is chasing down the 24/7 Champion, and has even won it four times. However this is all beneath someone like him, who has the whole package to be a main event player.
While WWE has damaged him quite a bit on RAW and SmackDown, I don't think it is too late for him to not only return to NXT, but be the top heel on the show to. He just has that natural charisma to do so, if given the right push and reintroduced the right way.