This is, of course, a matter of personal opinion. My own view is that Donald Trump is the worst candidate for president. I say this because he is not running on a set of policy positions. Any candidate who is running based on actual policies that they support is superior to him. The only policy of Trump’s that we know about for sure is his immigration plan. Outside of that, his main arguments are that A) he is so smart that he will be able to get everyone to do what he wants and that B) he is so rich that no one will be able to influence him by giving him money. I see this as a dangerous platform because it is completely out of touch with reality. A president cannot govern by superior intelligence, even if Trump really has that. A president needs policy positions and a president needs to be able to deal with and compromise with other leaders. Trump shows no signs of having many policy positions or of an ability to compromise with other leaders. He would, in my view, be the worst possible candidate to choose.
I am not completely impressed with any of the candidates. If I had to pick the one I think is best right now, I would probably pick John Kasich, though he has little chance of winning. While he is more conservative than I am, he is not a complete radical by any means. He has done a fairly good job of governing an important state. He seems to be open to talking to and compromising with people who disagree with him. These are the most important attributes, in my view, for a candidate right now.
Overall, I would prefer that a Democrat wins, but I do not necessarily trust Hillary Clinton’s honesty or judgment and I believe that Bernie Sanders is too far left to govern effectively. Therefore, I prefer a moderate Republican like Kasich. However, it is much easier for me to choose the worst candidate than the best.