There really isn't any qualified presidential candidates in this election. But, I would say that Donald Trump is the most promising candidates. Clinton, and Sanders have both had their time in congress, and they were lackluster at best.
So most promising for Trump means that he has a clear slate, and because the bar has been set so low in the last several elections, he should easily clear the bar.
He is the most likely to cross the isle and that alone would give him a win that no other recent president has been able to accomplish. It is a gamble with an unknown, but it can't be any worse than the best that can be accomplished with the known of Clinton and Sanders.