Among those rather quite (in terms of controversy) but highly-respectable projects, it appears there really isn't any FLOSS DBMS system that compares. It even bills itself the most advanced open source database on its main page.

I've had great honors for the project for years now, but what prompted this post is its 2013-04-04 Security Release FAQ (via), a highly-detailed and thorough explanation regarding an important security issue affecting a few of its releases. Reading this, one gets the idea that it's some serious developers running the project, and I deeply appreciate.