TOML is a worthy contender. It is my favorite simple but powerful-enough data language.

Here is a side-by-side comparison of data in TOML versus YAML: https://gist.github.com/oconnor663/9aeb4ed56394cb013a20

And some comments that resonate with me:

  The yaml spec is overly complex and parsing it properly
  is a nightmare. I rather prefer TOML because of it's
  simplicity. Unless one really need the gazillion extra
  features which yaml provides (which one probably doesn't),
  I'd say sticking with TOML seems to be the saner choice.

  I've recently kind of changed my mind on unquoted strings.
  They're nice when you're editing config files by hand, but
  they run into parsing issues in simple cases like when the
  string looks like an int, or of course when the string
  contains quotation marks itself.