Do you want there to be viable third parties, but don’t want to hand the presidency to someone you despise? It’s easy. It’s called strategic voting, and it worked wonders for Canadian liberals in 2015.
Do this: If you are a progressive in a deeply red state, vote Green. If you’re a conservative in a deeply blue state, vote Libertarian. If you’re in a swing state, vote for the major-party candidate closest to your values (you swing-staters are the only ones whose votes will actually determine the next president). If your state matches your major party’s politics, vote party line (Democrats in blue states should vote Clinton; Republicans in red states should vote Trump).
Here’s a handy state-by-state chart for progressives; conservatives can flip it.
Here’s why: in a blue state like California, conservative votes will not keep Hillary out of the White House, because she is likely to win California by a large margin, taking all of that state's electoral votes with her. Trump won’t spend much time there because he knows this. But Gary Johnson desperately needs those conservative Californian votes if there is ever to be an alternative to the Republican party. If he gets more than 15% of the vote, the Libertarians will have real influence. That would be very good for conservative politics going forward.
The reverse is true in Louisiana: a vote for Hillary is a waste of a progressive vote - it won’t affect the outcome. But that same vote has huge value to Jill Stein and her Green party. A strong viable Green party would be very good for liberal politics going forward.
The most broken thing about American politics (OK, one of the most broken things) is that the two major parties collude with one another to keep third parties out of the process. 2016 is a chance to fix this without affecting the outcome of the presidential race.