Like someone recently said about standing up for your convictions in a choice between bad and worse.. if you don't vote, you vote for worse and if you throw away a vote for 3rd that has 0 chance of winning it is vote for worse.
If you can't see it that way, think about this one. One candidate will likely cause more harm than the other. Common sense says to vote for the one that will cause you the least harm. Then go to work even harder for your other option of 2016 or 2020.