#1 Elias
Even as a heel, Elias has already proven that he can get over with the WWE universe, despite the fact that he's not the most talented wrestler from bell to bell.
The now former WWE 24/7 Champion has one thing that most people on Vince McMahon's roster do not, which is a very strong character. Simply put, WWE fans know exactly who Elias is, which is why he gets such a big reaction whenever he appears.
If WWE ever fully commits to Elias as a face, then he could end up being one of the three biggest stars in the entire company. Then, who knows? Maybe he'll vastly improve his wrestling skills, which might shoot him right to the top of the company.
Of the current heels on WWE's roster, Elias probably has the most upside as a face, so hopefully, the company will make the move sooner rather than later.