Having worked with a bit of YAML, RAML,(which is a superset of YAML) and JSON style configs/schemas... I'd take JSON over YAML if only because it seems to be more expressive.

Still, everyone forgets HOCON [1] is a thing, which solves many of the problems expressed here about JSON -for configuration-. It's easy to clearly specify things like time, reference other parts of the config, or if you want to change just one value, you can add that to the 'end' of the HOCON file and be GTG.

[1] - https://github.com/lightbend/config/blob/master/HOCON.md