In fairness to both of you, while chromatic is correct, and there is a PostgreSQL gotchas, it only has two entries, while the MySQL gotchas is a lot longer.

MySQL is highly optimised for data retrieval, and is often the best choice for write-once read-many databases. This is what I ususally have, so I use it a lot. It is not necessarily the best choice for other situations. However, if you know it well, it is quite well-behaved.

PostgreSQL is closer to something like Oracle in functionality, but that assumes that Oracle is what you want. Sometimes you do, but quite often you don't.

There's a nice discussion from Philo Vivero has an interesting (and similar) perspective.