What matters to me is how fast they work with Python, or in particular Zope. I need to make my own benchmark of MySQL and PostgreSQL with Zope and all the various database adapters.
The reason I moved from MySQL to PostgreSQL was partly because PostgreSQL has more enterprise features and that my colleges use PostgreSQL. But I suspect that for many of my projects I never even use these features.
Then I also found this from a Zope mailing list:
>The speed comparisions with PostgreSQL are very much an apples vs. fish
>sort of thing: the pgsql server was not tuned at all, and does a whole
>lot more that was never tested, such as multi-user writer access.