For small use cases, e.g. Hacking on a developer workstation, MySQL has historically been a lot easier to get started with. No need for Cygwin which used to be the case for postgres, MySql has a GUI installer, mysql has a ton of online help resources, no mental drain to deal with up front - how often should I run a Postgres vacuum? How should I schedule it?

When it comes to scaling up though, Postgres has in my experience, always just worked. This has been true for years. The documentation is excellent and the community extremely helpful and knowledgable.