Storing JSON as String or Embedded ORecord?

[Eric24]

If I need to store JSON in an ODB record, but I don't need to query within it (i.e. various JSON content treated as opaque by ODB), is it more efficient to stored it as a string or as an Embedded ORecord?

On a related topic, where is "@type" and its acceptable values documented? I can't find it anywhere in the online docs.