When should I use relational vs NoSQL databases?
What is the task you need to accomplish?
Frequently this question is asked as a "what should I use for a web app" question with no real details for what kind of data is being stored. As it turns out, that's ok! We actually have a type of database which directly fits "general purpose", by being fully robust and flexible. These are the relational databases, which are designed around the SQL standard.
Because "general purpose" covers most tasks really well when it comes to databases (something that's not nearly as true in other areas of technology), you can just grab PostgreSQL or MySQL and use that for all data storage purposes, and likely have no issues for the full lifetime of the project.