MariaDB compared to postgres is a difficult choice, both have a multitude of features. MariaDB 10 was a game changer for the mysql landscape.
To make postgres 10 as easy to scale as mariadb 10, and for query semantics in mariadb 10 to allow for the complexity that postgres 10 allows; both require tradeoffs in management tooling, development practices and understanding.
Neither of them are a silver bullet. They both require effort, like any RDBMS. But both are great choices.