Databases: which one to chose?

A rundown of databases from a qualified source:

• Oracle: everyone knows it, functionality for just about everything but doesn't do anything well
• SQL Server: The poor man's Oracle: not as much concurrency, better user interface
• Access: WORST!!!! No concurrency control
• DB2: Faster than Oracle, UI tools and SQL is not as robust as Oracle's
• Sybase: Good, but dying out because of market share
• Informix: Very good, but bought out by IBM and integrated into DB2 (prof's favorite)
• MySQL: Up until 5 no support for a lot of things like foreign keys and indexing, free
• PostgreSQL: Robust database, free
• There exist other, specialized databases for streaming data
  

The free ones: MySQL vs PostgreSQL:

• MySQL:
• Larger development community
• Just a tiny bit friendlier
• Better for query-intensive work (reads)
• Use InnoDB storage engine for ACID compliance, not the default engine, MyISAM
  
• See other popular options, such as clustering (synchronous) and replication (asynchronous)
• See this thread for comparison
  
• Administer using PhpMyAdmin or others
  
• PostgreSQL:
• 5 years ahead of MySQL (but MySQL is catching up fast)
  
• Perhaps able to handle double the data?
• Data type storage more optimized
• Better for update-intensive work (writes)
  

Other advice:

• Cache large/popular files: look at Apache's cache setup
• Verify that files have type, non-virus integrity

Links:

• Comparison of Oracle, MySQL and PostgreSQL