Sandow or RyBack. Sandow is Triple H's pet project, RyBack is Vince's pet project. Take your pick. It's Sheamus vs Orton/Batista vs Cena round 3. Who will have their project win? At the end of the day, they both will, it's only a question of who wins MORE.
Outside choices are Cody Rhodes or Dean Ambrose, because of how young they are. Dean is extremely unique unlike Cody, more charismatic by 20 lightyears, mic work isn't even comparable, he's world's better. Cody on the other hand has the advantage of having a name in the business as well as having racked up a tenure in WWE already, which would mean he's capable of ascending to the main event faster in the short term, but not the long term. Both of these guys will have big futures, of course Ambrose needs to be called up first, which will never happen seemingly. These are the next in line.
Jinder Mahal is going nowhere. He's out.
Brodus Clay is going nowhere. He's out.
Cesaro is unknown at this point. He could either be a break out star or a low card flash in the pan, either is possible. Either way he won't be THE biggest. He's out.
Sin Cara can't speak English, which automatically handicaps him for major success, as well as him not clicking with WWE style and always feeling like an outsider. He's out.
Ziggler is always booked terribly. Always. Even as a main eventer. He's out.
Wade Barrett is who it really SHOULD be. It won't be. He will never be a major star or a world champion for that matter. We all know why, let's not try to pretend. He's out.