What SQL to Use for Sharepoint 2010 Express Database?

Hello Techyv Friends!
Have anyone tried using Sharepoint 2010 Express Database? Can anyone please tell me what Structured Query Language or SQL databases are better suited for Sharepoint 2010? I am currently using MySQL and MYSQL. I am also familiar with Postgresql. Do you think these are compatible with Sharepoint? Have you tried using any of these databases with Sharepoint? How is your experience? Have you encountered any problems? Your comments are of great help.
Thanks!
