just my experiences (running multiple Joomla 3 and 2.5 sites on COS).
Initially I set the ownership to apache:apache
First component I install on Joomla is Admin Tools.
This extension has a 'permissions configuration' and a 'Fix permissions' button that will set al rights correct for your Joomla site: no risks in setting rights wrong when doing it manually.
it also has a 'Database Tables prefix editor' and 'repair and optimize tables' button: super stuff.
