The Couchbase team did a great job putting together this fairly-reasoned analysis. It gives side-by-side comparisons of Postgres’ JSON query syntax and SQL++/N1QL, which is the query language used in Couchbase. It touches on indexes, performance, ergonomics, and finally where each is a good fit.
I’ve personally found that Postgres’ JSON data types provide just enough document-orientation that I can sprinkle in where it makes sense in our data models. But, as with all things in developer-land, YMMV!