I believe everyone who can vote should vote. This "I won't vote" option is complete bs. If you don't vote your not participating in our government which is not only your right, but your responsibility. If you don't vote you don't get to complain about the outcome.
As for third party candidates, I'm sorry folks but the US is solidly a two party system. In November any vote not for Trump is a vote for Hillary. Any vote not for Hillary is a vote for Trump. It's been this way for longer than I've been participating and it will continue us to be that way long after we're all gone.
Carefully weigh the differences between the candidates and what they stand for and make your decision. Cast your vote.