"PostgreSQL is one of the most widely used open-source relational databases, and is seen by many as a good alternative to more-basic systems such as MySQL or MariaDB."
Apart from anything else, it simple scales better. MySQL is good up to a point but its memory consumption quickly grows out of control.
I have a 48Gb box which was struggling on MySQL (350 million records). PostgreSQL is working very comfortably on it, using less than 12Gb.