Unfortunately Mongodb has serious security problems, and has had data retention issues in the past and honestly very slow for map reduce, search and math. I’ve deployed 6-9 apps on MongoDB and I like it for some things, but in my day job we have been urged to move all apps off of Mongo as soon as possible so when it comes to my hobby projects I am veering away from it now completely.
Postgres is vastly more feature-rich, time tested, performant, and out-performs Mongo for most NoSQL operations. I will switch frameworks before I switch the datastore. Languages come and go, but data storage is too important to make concessions on, and with Postgres there is no compromise, it just does exactly what I need it to do.
Now if only Ecto were as feature-rich 
