JSON if it also has an online schema, and a reference to it in the JSON file. That way some editors can check for errors and hint to the user about it.
But the good old flat text-data, the ini format is consistent, readable, and easily understandable by less-technical users.
I'm no fan of XML. It looks messy and the schema is difficult to write, imo. XML works best as a markup language.
YAML could have been okay if it were stricter with what they consider strings, and used tabs instead of spaces.