YAML is bloody terrible, and I've hated it since the first time I was forced to use it.

JSON or TOML are always preferrable, based on the use-case. If you want humans to be able to change the file, use TOML. If only machines and debug programmers need to see the file, use JSON.

YAML is in this horrible in-between where it's extremely unintuitive at first glance and it's really easy to break. The only positive aspect to YAML is that it's legible. But legible is not the same as understandable. TOML is just as legible, but it's also easy to understand and change. JSON is hard to read and hard to understand, but the structure is very durable.

I'm going to take a guess here and assume that there's a strong correlation between people who like Python and people who like YAML.