PostgreSQL is the better default for new applications, and MySQL fits when a CMS, host or team already requires it.
On one million rows, PostgreSQL 18.1 was 7.9 times faster on a scan rollup and 12 times faster on a join than MySQL 9.3, and primary-key lookups tied.
PostgreSQL's table and indexes took 108 MB against MySQL's 87 MB, so check the storage cost at your scale.