Chances are, they choose Ryback or Sheamus. A great dark horse would be Daniel Bryan on some Angle steeze.

Sheamus doesn't need to be a heel to be enjoyable. He can be a great babyface with an edge, which he already has. They just need to cut out the jokey-joke persona. He's one guy who can match Cena power for power, and he'd make a credible threat. They'd have to to insulate him with a major feud (Punk?) while just missing Cena everytime it looks like they're about to cross paths until that last three months when it's time to finish things. Cena catches a White Noise, the Celtic Cross makes a return, and gets a Brogue Kick to finish things- except Sheamus thinks better of it and picks Cena back up for a second Brogue Kick to make sure.

Ryback could work depending on how he develops from here, but right today I wouldn't pick him for that role. There's also a possibility one of the Shield gets a face turn (I'm betting on Rollins, personally) and Chris Hero is still waiting to get called up to the big show.

The scenario I'm talkig about is a minimum 1 year arc before it comes to a conclusion, so there's plenty of time to position someone. I like having well laid plans, but something like this needs to be fluid and 'that guy' needs to happen naturally.

Ziggler could make an amazing face. The best of the best could play either role well and he's got enough fans to make a complete face turn work at some point, especially if he gets a long reign as champ.

Bryan could make for a huge face at some point though, and I like him for this pick. He'd represent all that's good about the WWE, embrace the fans on some coming out through the crowd shit, and the YES!!!! chants are a major marketing factor. Plus, he's got the indy crowd behind him. Yeah, the douchiest of that crowd will turn on him but I'd bet most will stick by him. He's another Kurt Angle type and has massive potential IMO.