Following the latest contests it is realistically a fight between Trump and Cruz. Trump is ahead on delegates but by fewer than a hundred. Cruz is very right wing, against abortion etc. and would tear up the deal with Iran over nuclear weapons which is not only imbecile but would isolate America internationally without a single ally except Israel.
Trump says outrageous things, dies his hair and winds people up. But he cuts deals and has a shrewd judgement of the other side’s red lines and would do better than everybody thinks on the international stage, especially with the Russians. Domestically it is hard for me to judge. But what he says to get votes and what he does may be not quite the same. Again he would cut deals. His fortune is estimated at between $ 4 and 10 billion and you can’t get that kind of money if you are clueless.
I would sum up the difference between the two this way. Cruz is driven by ideology. Trump is driven by outcomes. Oh and Rubio? He has not yet learned how to drive.