If I feel the need for any kind of serious Database, I will always choose Postgres. Postgres offers the full power of a Relational Database, with the flexibility of a NoSQL Database thanks to its Jsonb data type. Postgres is also ubiquitous, with support for it in every programming language I have used to date. There are some phenomenal tools developed for Postgres, such as pgcli and pg_flame. While I tend to use Mongo for simpler projects, Postgres is absolutely my go-to Database when any type of complexity is involved.
"Postgres is the one, true database"