1. Johnny Gargano
Sometimes the most obvious choice is the best, this is because Johnny Gargano's pursuit of Ciampa just makes his antagonism with Black organic. It was due to Gargano's fault that Black lost his title and Ciampa gained it. That same passion drove Gargano to a match with Ciampa and Black. However then Black got attacked.
The champion denies it and it's believable, Gargano, however, hasn't much to say. He's lost favour with the crowd over his actions in costing Black and his thirst for revenge on Ciampa has turned him into the very same devil he faces. In many ways, Gargano will provide the most interesting and subversive arc for any face of NXT.
Much like Sami Zayn before him, he is an underdog with a ruthless friend turned foe. There is heartbreak there but there is also a drive to destroy Ciampa to the point of mutual ruination. Black got caught in that turmoil and Gargano wanting to right his wrongs, did the greatest wrong he ever could.
Gargano attacked Black and there are no two ways about it. Once revealed he will face the consequences. There's no heel and face here, there's just a character, a man seeking vengeance, losing his soul and hopefully one-day finding redemption in his actions.
That's the day that once again fans shall chant 'Johnny Wrestling'. Till then Gargano better jumps quick into the black mass in this abyss of a downfall of his own making.