I think it's horses for courses. JSON I guess is the best for interchange i.e machine to machine, but I never want to edit it by hand; XML is relatively easy to read but can be quite painful to edit raw, but it can be quite easy to develop a structures editor. I’d favour it for document persistence. YAML is fine for configuration files but I would be careful about how I apply it and would always provide it as a heavily documented templated config file. YAML when used correctly is by far the easiest to edit in the clear, with a plain text editor. With that said, I would try to get away with basic namespaces properties files first before I’d go that far ...
ini if needs are crazy simple, YAML if you need a structure like JSON's but with something any human ever needs to interact with. JSON if humans aren't in the loop.
TOML, in my opinion, is like a weird mishmash of JSON, ini, and bashisms. Though I have worked with it a lot less than the other formats, so YMMV.
Try writing strings with backslashes, or adding a new line to your array and accidentally leaving a trailing comma (or accidentally forgetting it for the previous row). It's also just very visually noisy. I agree with a lot of the other comments in this thread that for human configuration: TOML > YAML > JSON > XML
You can edit JSON by hand but it’s not what it’s for. It’s not designed for that and it’s not really suitable for that. Theoretically you can milk anything that has nipples, but you might find the experience of milking a cat to be ... challenging
