The Strange Thing About the Johnsons gets all the attention among Ari Aster short films, because it has the most alarming premise and is perhaps the most disturbing as a result. But I think of the ones I've seen so far, Munchausen feels like the best. It's Aster doing a silent movie, and using sweeping music and bold, saturated colors to tell a bleak and tragic family drama story. The effect of it all felt striking to me, and I liked it a lot more than I thought I would.
Going through some of his films chronologically at the moment, this might be the one where his style was really starting to take shape, and it feels like it deals with the sorts of family issues particularly found/explored in Hereditary and Beau is Afraid (and often feels like it foreshadows the visual style of the latter). It's disturbing and downbeat in its own way, but I think benefits from not going quite as far in that department as The Strange Thing About the Johnsons (which I still like, or at least have a certain amount of respect for).