Not much idea about it but I think default available will be more suitable for us to practice atleast for the time being.
MariaDB has many more optimizations as compared to MySQL.
But since MariaDB is a fork of MySQL, therefore the database structure and indexes of MariaDB are the same as MySQL.
Will recommend that you go with the DB that you are most comfortable with. There is not much difference. Please note that all the operations require Read / Write.
Using a separate Database server with a good configuration that will handle the Read / Write requests, with SSD / NVMe drives actually helps in speeding up the working.
Usually, the DB server is on the same machine with the web server. For medium sites (upto 200 concurrent users), it works fine. Performance is thus not limited only to the type of DB used.