It's very easy to dislike both candidates in play today, and certainly feels good to vote for neither.
But they are not equally bad. One candidate views large swaths of Americans as inherently illegitimate, while the other is perhaps garden-variety corrupt.
Your conscience is what stops you from doing things that feel good, but hurt others.
It also stops you from doing things that feel bad, but are rationalized backward to be the "right thing".
I assure you, both Clinton and Trump in the White House will be equally bad. Just a different kind of bad.
Vote for Gary (or Jill)!
Because people made a similar decision to what we're talking about now, a majority of voters saw their least favorite candidate win, which many found to be an unfortunate result.
As others mention, this is fixable if you can rank your choices, but until then...
Nothing was altered. You vote your conscience.
It's when people start playing games and vote for the less bad option because they don't want someone else to win that we get these kind of ridiculous candidates. Each candidate will take ridiculous positions and then essentially blackmail the electorate with "what are you going to do? vote for the other guy?". That is not a healthy recipe for a democracy.
There are no 3rd party candidates. There are only candidates. Vote for the one you actually want. There's plenty to choose from.