I'm genuinely non-snarkly interested in the other commonly used alternatives your mentioning, in addition to json, anything else you recommend looking into?
I'm really digging YAML as a serialization format. I haven't ever used it with web applications, so I don't know what kind of tools might be available for that.
TOML and YAML are nice as human-readable configuration formats; Protocol Buffers/Cap'n Proto are really good if the schema of your data is strongly defined.