you're effectively voting for the republican
No, that's only somewhat true if it's a tight election. If your area leans heavily to one side or the other, your vote for a third party signals that neither major party candidate is acceptable. If those votes get high enough to start impacting elections, they'll change their policies/candidates to attract new voters.
AFAIK, most people live in areas where one party is expected to win. So if that describes you, vote your conscience. If you live in an area with tight races, you may want to choose the less bad among the two major candidates. In both cases, push for voting reform, ideally something like Approval or STAR voting. That way you can vote your conscience and fall back to the major party candidate you prefer.