Depends heavily on the data. If it's human-readable, read-only, and almost completely unstructured, plaintext. If it's human-readable, read-only, and structur

Depends heavily on the data. If it's human-readable, read-only, and almost completely unstructured, plaintext. If it's human-readable, read-only, and structured but formatting doesn't matter, HTML. If it's human-readable, read-only, and formatting matters, PDF. If it's intended for humans to read and write via hand-editing, and then subsequently have a machine work with, then TOML. (Never YAML.) If it's fundamentally tabular, CSV. (Never XLS.) If it's an API result from a web API, reluctantly JSON; as much as I'd prefer TOML, JSON is more universal.