Have used both. Depends how you use them.

If you use jsonb of postgres to just dump things you don't query on, it's fine. If you try to cheat and dump your mongo schema into a jsonb field, you're gonna have a bad time.

JSON queries in postgres are, IMO, extremely nonobvious. It seems like any time we wanted to run some rather simple report that involved json fields, some poor dev had to spend ten or more minutes figuring out the correct syntax to do so. Mongo is an absolute breeze in comparison.

Person opinion? JSON doesn't belong in the db, make a proper schema. If you don't want to do that, or don't like or want to learn SQL, just use Mongo or some equivalent.