I always thought Postgres was the one that did correctness first, then performance, while MySQL was the inverse. I also enjoyed Postgres documentation. But in practice I have very little experience with MySQL, but I do recall it liked to silently coerce invalid dates and its UTF-8 wasn't quite UTF-8.

And MySQL apparently still doesn't support transactional DDL (i.e. BEGIN, ALTER, ALTER, UPDATE, COMMIT), which is quite nice for db schema version migrations.