If you don't like either candidate, a write-in vote is the proper response, much better than not voting. A write-in vote will not win, but it sends a strong message that you don't like the candidates. If you don't like the parties candidates, you won't provide financial support and they are every bit as interested in that as they are your vote. Also a large write-in vote can be a precursor to the rise of a third party.I certainly understand where you're coming from, but I won't allow myself NOT to vote. By doing that, I become part of the problem. I have an obligation to myself and my family to make a choice. It may not be the choice I want, but it will be the best choice given the options I'm handed.
I typically vote on principal in primaries where it can possibly count. When it comes to actual elections, writing a name in might send a message, but it might also allow a candidate I do NOT want to get elected. If all I have is a choice between two evils, I will choose the lesser every time. To not do so is an act against my own interests.
It is also possible that a person you do not want to get elected will win anyway.
So vote your consciousness, not your fear. That is the only way you can get what you want.