Dean Ambrose should not be champion. He doesn't look credible enough, I don't think he's ever won a singles feud in WWE. He's barely won on pay per view. His selling is just the worst. The scripts they give him for his promos are terrible. And I think fans would cool off on him a lot if he won the title out of nowhere. His underdog status is a lot of why people still really like him.
I'd like to see Reigns turn on Ambrose and win the title in the process. Or if they're keeping Reigns face, then have Ambrose turn heel on him - it might jump start the character a little. I reckon he'll work more naturally as a heel anyway, it's harder to play the loose cannon character as a face. I think Ambrose has potential to be a top guy, but he's less ready for it right now than Reigns is.
Other people will disagree, as many people are higher on Ambrose than I am, but I just don't want to see him in that kind of spot until we see more from him. As much as I don't love the idea of Reigns as champion right now (at least as a face), Ambrose as champion would be worse to me.