Trump, of course, is awful, but I'm also not at all a fan of Ted Cruz and I think his ideas are as extreme and wrong as Trump's. He just packages those ideas more nicely and I think that Trump is far more likely to be able to govern effectively (even if he's trying to implement things I very much disagree with) than Cruz. Of course, then maybe I should hope Cruz is the candidate.
Actually, I'm just pleased Rubio did as well as he did in Iowa. If we're stuck with one of these three, then I'd rather Rubio. Cruz's and Trump's immigration policies are extremely similar with no plan for what do to for the millions of undocumented people living in the US; Cruz's plan has some real problems (he needs better incentive for people to register, for example (also, he needs to make his website more user-friendly rather than making people slog through long quotes from some book he wrote) but it also does far more to address helping people who are undocumented and that's a good thing. I'd also prefer his foreign policy goals to Trump's or Cruz's even though I disapprove of many of them.
But Bernie and Hillary? No idea what will happen there. Bernie is a good man and I like that. But he's old- 75 in November. And I'd much, much prefer to have Hillary running US foreign policy (Bernie doesn't even have a foreign policy section on his issues page). She knows how the system works, she's pragmatic, and she knows how to get things done. Bernie is exciting but I'm not sold that he would make a great president (or that his ideas would go anywhere if he were elected). Also, I really like many of Hillary's proposals- they are far broader and reach a much more diverse population than we're used to seeing, and I think at least part of that is because she is a woman.
No idea what will happen and it'll be interesting to watch it unfold, both from DC and Riyadh.
ETA a couple of days later the Rubio's criticizing Obama for visiting a mosque and calling for religious tolerance moves him neatly in the wacko box with Cruz and Trump. I'm not a fan of Bush, but he has often at least said something reasonable when another Republican candidate says something crazy (saying that the president visiting a mosque is the right thing to do after Trump and Rubio attacked the idea, saying we welcome immigrants after Ben Carson goes off on them in debates, etc.)