I favor the "shut up and calculate" school, which says any interpretations that don't make actual predictions are both unnecessary and harmful.

Certainly, if you have to choose an "interpretation" and tell stories about other universes we can't interact with, MWI is better than collapse, for the reasons Eliezer gives. But I don't think we should have either of them.

I agree that it doesn't make sense to privilege either their existence or their nonexistence

It's not a matter of privileging. Existence is not an applicable predicate. It's not that we don't know whether they exist. Just as other universes are neither sweet nor sour, neither happy nor sad, they neither exist nor not-exist.