Also, if you use Postgres on multi-CPU machines, it's faster than MySQL. But, make sure you read this:
(comparison of Oracle/MySQL/PostgreSQL)
One last word of advice if you end up using PostgreSQL, learn and use this:
Finally, we are moving back to MySQL because we found a really fast replacement for the MyISAM storage engine (a lot faster than Postgres) and our part-time DBA knows MySQL and this new storage engine a lot better than Postgres. We are also moving to VPS architecture and Postgres' performance advantage over MySQL on a VPS doesn't really exist.
In the end, go with what your staff/friends know and what your hosting place recommends. If they have an optimized DB stack and provide some kind of a support for it, stick with that DB because you can always go to them for help!
When you say that "Postgres' performance advantage over MySQL on a VPS doesn't really exist.", I'm not sure what you mean: DBMS performance is a complicated subject, and significant performance differences exist between MySQL and PostgreSQL on essentially ANY hardware platform. For example, if your app uses complex queries with a lot of joins and subselects, Postgres optimizer will likely give you significantly better performance than MySQL's, regardless of whether it happens to be running on a VPS. Similarly, MyISAM's performance with an update-intensive concurrent workload is going to be pretty bad, regardless of the hardware platform.
What are your thoughts and the database of your choice?
Also, for their MySQL test procedures, I could not find any information regarding which storage engine they were using. InnoDB is fully ACID-compliant, whereas MyISAM has reduced overhead since it does support transactions and foreign key constraints, for example. I found a good article, http://www.mysqlperformanceblog.com/2007/01/08/innodb-vs-myisam-vs-falcon-benchmarks-part-1/ , comparing the two storage engines, and the results were pretty surprising to me.
It ultimately comes down to your individual usage patterns. Using a database abstraction layer will allow you to test your application against different databases so you can see how your application performs first hand.
We could spend all day on this, though.
Basically, databases have been well-commoditized, like Unix, HTTP servers, and hosting. If your needs fit their common usage scenarios, you should just go ahead and use them.