I suggest that you try Postgresql out for a project, and see if you like it . This is more or less how I came to be using it.
Of course you can test drive Mysql similarly...then make up your own mind.
Due to the strong feelings of the various communities, you will probably become buried in opinions if you read too much about comparing Mysql and Postgresql. Be warned that you will become buried in marketing drool if you read about comparing Oracle to anything at all!