Nobody would have ever looked at The Ringmaster or Rocky Maivia and thought that they would both end up becoming the mega stars that they did. And I know Austin in ECW was sort of playing the Stone Cold in it's earliest form, but doubtful that any saw what would become one of the biggest draws of all time. Even less so when you looked at his work (which was good) as one half of The Hollywood Blondes or his work as The Ringmaster. No one ever saw Rocky Maivia (the worst kind of smiling dick baby face) as someone who would transcend into a successful movie star as well.
My point is, it's sometimes impossible to tell who really will catch fire with just the right push or gimmick or angle or whatever. So I usually have no real strong opinions on who will be the next top face. That said, I don't see Ziggler or Bryan in that role at all. Both are workhorses you can rely onbut I don't see them going past WHC gold. To be the face of the company like the holy trinity (Hogan, Austin, Rock) or like Cena and Batista, you need a larger than life character or prescence and they don't strike me as having that.
I would say Ambrose but I see him as more of a natural heel than baby face.