#1 Aleister Black
The darkest character in NXT vs the brightest character in WWE. This is a match made in heaven (or hell) that WWE must capitalize on. Black and Cena are characters that are polar opposites, and that is what makes them the perfect foil for each other.
Black can go the Bray Wyatt and Kane path and try to make Cena embrace his more human instincts of anger and the need for validation. Unlike how it turned out with Kane and Wyatt, this can actually be effective within the NXT landscape where Cena's character won't be tightly scripted.
Check out which wrestler EC3 finds cute RIGHT HERE
Black hates the facade that Cena portrays, whereas Cena is trying to show everyone that it isn't a facade, but actually who he is as a person.
Black is a passive figure just telling Cena everything as fact, which does cause Cena to doubt himself. This self-doubt is driving him crazy, and he wants to prove Black (and himself wrong) by facing him one on one.
The match has tremendous story-line potential for both men. Showing Cena fight not only Black, but also himself is an angle that can absolutely change the match. It can make it go from great to absolutely epic.
Black is never overly aggressive, choosing to continue his relatively calm character work as he is watching John Cena self-destruct under the pressure of his own being. However, that mood changes as Cena gets more and more aggressive.
Cena is given the chance to end the match, as he could break the rules and possibly finish it off. This self doubt cripples him, as Black takes advantage of this and defeats Cena.
Even as all feuds up till date have had open endings, Black needs to triumph here to show that Cena is not the same person we all see him to be. Where WWE and NXT go from there is up to them.