Json with comments is literally perfect. Formattable, machine parsable, minimisable, easy and fairly concise. Honestly I can't think of anything better. (Comments in json are essential IMO, without it it's actually not that great, and I'd go with yaml instead)

I know it’s kinda cheap, but for me nothing is the answer (that includes hcl). I’ll use what I find, but I can’t say that I love anything.

If something uses toml, I will use toml. I’ve also used json-schema in the past.

Depending on what I do I find yaml and kustomize okay, etc.. Using something like client-go has its advantages as well.

If I am building something from scratch then I would reach for a simple ini. I feel like everything else overcomplicates things and that’s usually a symptom for something else.