The problem with this question is that these labels are all in widespread use by/for people who don't really fit the academic definitions. A "democratic socialist" might be a social democrat or a stealth tankie. A "libertarian" might be a traditional conservative, an anarcho-capitalist, or a stealth fascist. Someone who identifies with the "alt-right"...well, they're pretty much all fascists, but some are more immediately dangerous than others.

If I had nothing else to go on, I would probably pick the "democratic socialist", at least in North America and Europe. But there are a fair number of specific "libertarians" whom I would prefer over specific "democratic socialists". The one thing I can't imagine is choosing an "alt-right" person over the other two.