I'll go with Postgre SQL over mySQL just becuase its been offering sotred procedures and such like for longer than mySQL has been.

I've only ever used Postgre for Java apps and would never consider using mySQL for that just because Postgre is really good theres no reason to change, I know mySQL 5 has stored procedures but I've not used it as of yet for a few reasons really the main one being that upgrading to mySQL 5 will kill a few of my apps