There are a couple I have in mind. Like many techies, I am a huge fan of RSS for content distribution and XMPP for federated communication.
The really niche one I like is S-expressions as a data format and configuration in place of json, yaml, toml, etc.
I am a big fan of Plaintext formats, although I wish markdown had a few more features like tables.
People bitch about YAML but for me it’s still the preferred one just because the others suck more.
TOML like said is fine for simple things but as soon as you get a bit more complex it’s messy and unwieldy. And JSON is fine to operate on but for a config? It’s a mess. It’s harder to type and read for something like a config file.
Heck, I’m not even sold on the S-expressions compared to yaml yet. But then, I deal with so much with all of these formats that I simply still prefer YAML for readability and ease of use (compared to the others.)