Even if you'd rather not have either, and don't want to vote for an independent, go for whichever you feel does the least damage.
It's worth everyone remembering that there's still a vacant Supreme Court seat left in the wake of Scalia's passing in February. And not only that, for liberal Justices, Ginsburg is 83, and has fought some battles with cancer already; and Justice Breyer is 77. That's two liberal Justices who could plausibly fall ill enough to be forced into retirement, or die, as Scalia unfortunately demonstrated. In addition, Justice Kennedy, the somewhat independent member of the court, will be 80 by July. That's a whole lot of Supreme Court Justices who may be going in the next Presidential term.
If you include whatever happens with Scalia's vacant seat and what comes of Garland with the next presidency, the President could theoretically be in a position to nominate 4 Supreme Court Justices. For either side, be it Republican or Democrat, there is a serious opportunity to shift the court into favoring their ideology for decades. We will probably be looking at somewhere between 20-3o years before an opportunity anything like this arrives again. And the results could be monumental, even if the liberal wing only fills in Scalia's seat with a left-leaning Justice, that's still enough to get Citizens United overturned, and a swift end to the era of Super PAC, among many other things. Conversely, the Republicans can probably wait out until Ginsburg is gone (She's fucking 83 years old after all), fill in Scalia's seat, and have a majority in the Supreme Court that would allow them to do much, be it over overturn Obergefell v. Hodges and get rid of nation-wide gay marriage, knock out more parts of the Affordable Care Act, or even possibly try to overturn Roe v. Wade.
Regardless of one's personal opinion and disgust with their candidate, there is a whole lot that can change solely based on what happens with the Supreme Court. This isn't something that can be changed if a Republican or Democrat wins in 2020, this is something that will be effective in the rule of law for multiple decades.