You might be wondering when to use relational and when to use NoSQL. Well, given the techniques and technologies in existence today, I would recommend you work with the type you feel better working with. NoSQL brags about being schema-less, scalable, fast, and so on, but relational databases are also quite fast for most of your needs. A few relational databases, such as Postgres, even support documents. What about scaling? Well, most projects do not need to scale as they will never be big enough. Others, just scale with their relational database.

If there is no important reason to pick one or the other for native schema-less support or full ACID support, either of them will be good enough. Even security-wise, there are no big differences worth mentioning. MongoDB has its own authorization scheme as most relational databases do, and, if properly configured, both are just as secure. Usually, the application layer is more troublesome in this matter.