After five years in Oracle’s MySQL team, Steinar H. Gunderson resigned a few days ago. On the same day, he dropped the bomb on his blog:
let me point out something that I’ve been saying both internally and externally for the last five years (although never on a stage—which explains why I’ve been staying away from stages talking about MySQL): MySQL is a pretty poor database, and you should strongly consider using Postgres instead1.
As @brandur appropriately puts it, in the world of software engineering, it rarely gets more definitive than that. And authoritative, I might add, given both the role he covered at Oracle and his overall track record. The whole short post is worth reading2.