There numerous problems with YAML. It is underdefined, ambiguous, fragile, and is just impossible to write a portable parser for.

JSON is naive, lacks almost everything. But is supereasy to parse and read.

As funny as it sounds, XML is overspecified. Parsing is possible and predictable but supporting the full standard (all of them) is so much work that nobody does it anyway.

So, given the choice above, i'd go for naive simplicity.