If we couldn't morally choose the lesser of two evils in a binary election (which our is), then Catholics would have to sit on the sidelines in every election, most probably, and that would be a morally perverse outcome.
Regarding the candidates: Hillary is corrupt. Trump is an un-PC executive. Johnson is not a choice.
Hillary: Mostly, I want to stop her from corrupting the system and making money off of her public service while driving the country into the crapper.
Trump: In my experience, being a good executive does not often correlate to being likeable. One of the best CEO's I've known personally would not be much more likeable than Trump as a person. He was funny at a company dinner (usually very un-PC, proabably because he was CEO and he could be, so he was), but he could be a challenge on a personal level. And yet, I would let him run my company any day. The guy could process information; he was flexible (non-dogmatic), but he was decisive. He understood risk: he could weigh it and adjust to it, but he was never paralyzed by it. Trump strikes me as very similar to that guy. His dogma, to the extent he had it, was dogma about managing people and operations, not dogma about specific outcomes (other than successful outcomes). This approach is foreign to politicians.
Johnson: Unless and until Johnson gets on the debate stage, he is a non-starter in this discussion. I don't begrudge anyone who decides to vote for him as an exercise of their free choice; but he doesn't enter the morality equation until he has a chance to win. Amazingly (given the other two candidates), he doesn't.