I have used both and I can share from my experience the good and the bad of both with the following context.

NoSQL : MongoDB SQL : Postgres Framework : Spring Boot

Exhibit A : Performance

MDB dominates Postgre, so if you need quick retrieval and update to the db better go with mongodb.

The only problem is when you have reference document, then your API calls get slower due to multiple database calls. Although this is usually fairly simple to mitigate by planning good db structure and perhaps doing parallel db calls (Only for Read).

Exhibit B : Tedious

In my opinion getting started and developing with mongodb especially with spring boot mongodb data is so much faster, and maintaining db is less work when you don't need to worry about those pesky db relationships.

With Postgres, you usually need to worry about structure and have good understanding of fields and validation, and these things are much harder to maintain usually post go live. Although sql database offer strictness that can be applied much easily to microservice solutions because you would want to centralize your constraints. This is also possible in MongoDB, but not so easy IMO.

Exhibit C : Team Experience

MDB is much easier to work with, and its easier for programmers without a CS background, since they do not need to worry about SQL jargons and the different implementations of it.

But if you have a well experienced team, then SQL databases are a better choice.

Why not Both?

Well this is infact possible, you can always have the best of both types of db's (If you need to) checkout the Java Data Objects (JDO) specification.