Trump. The man would commit an impeachable offense within a fortnight, while Cruz is an actual qualified politician. Whoever runs with Trump won't have the cult of personality, won't have an6 mandate, and will be a victim of the political process in every aspect. He'll be a great replacement.
I think that's almost a more interesting question, who would be Trump's running mate? Who would Trump want and who would accept? Edit: The obvious choice would be an establishment republican, but who would do it? Trumps supporters are old, uneducated white men and women. How would he get the young, educated people? That's right, a Trump Sanders ticket :)
According to the news of the past couple days, Vladimir Putin. Me? I'd hold out for someone truly awesome, like Herman Cain or Sarah Palin. But if I were trump, I'd find an establishment wingnut with an actual political history. Which means Palin, Santorum, Gingrich or Huckabee. All of which would be hilarious. Even better would be like Bobby Jindal 'cuz it'd only take a week for Trump to say something outrageous about immigrants.
The GOP does not depend on the young and educated. :( Or non-voters.
The best thing about a Trump presidency is that the left would shit itself. You would see 2 years of insane politicking, money raising and engagement to stomp him and his ability to lead, much like the 2006 election. The 2020 election would be fear, fear and more fear, but IMO a Dem. would win. No more Clintons on the ballot either, which is something that needs to happen now rather than later. Hillary would be a good president from the standpoint that she would get her agenda done, the problem I have with her is that her agenda is way, way to the right of mine. The problem with Hillary is that she is the ultimate boogeyman to whip the fundraising base. She fuels the NRA, Fox New ratings and Super PAC funding like nobody else.