Is voting for a third party candidate or not voting at all a cop out?

The US presidential elections, despite the presence of other candidates' names on the various ballot, is in reality a binary choice. Under our current system, either the democratic or republican party nominee will be the next president. No doubt about it. So what happens when a citizen just simply can't stand either candidate and doesn't want either one to be president?

Some people decide to stay home and just not vote for either. Some decide to vote for some relatively obscure candidate on the ballot or write one in. But it seems to me that in doing so one is in practical effect forfeiting their right to determine who leads the country for the next 4 years. No matter how bad the two choices seem, one is going to be president. Do citizens have a civic responsibility (is that even a concept anymore?) to make a tough decision and choose? Or is refusing to make that choice, and thereby leaving it in the hands of others a valid approach to elections?

My thinking is that no matter how bad both candidates may be, when you start going down a list of pros and cons, somewhere down the list you will finally reach a point where one candidate gets a slightly better mark than the other on something. Or maybe it's more broadly focused, like a desire to not have all three branches of government controlled by the same party. But ultimately there should be some difference to make you hold your nose and pick one over the other.

IMO to "waste" a vote on a fringe candidate or not vote at all is shirking a responsibility all citizens should be expected to exercise.