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!
best wishes
Mark