Mongodb was a lot easier to manipulate json in for a while vs postgres, but once postgres got json path support it evened out a bit imo.
Say you have some json and nested in it somewhere is an array of objects, and you want to just map over that and update those objects. I was writing a migration to do that in Postgres <11 once and it was not fun to try and figure out how to do it.
I haven't worked with Mongo in years though, so no clue how it has evolved since like 2015.
