I know they do a lot more than Facebook and YouTube, but I like to see good communication on social networks and that decided who I chose.
Thing to remember about pr is what it stands for Public Relations, i.e. relationships with publics.
http://prdefinition.prsa.org/
Also I find this article helpful.
http://stevefarnsworth.wordpress.com/2010/10/13/what-is-the-biggest-mistake-companies-make-with-their-social-media-strategy/
Social media is a fantastic tool for PR practitioners but it is not our only tool.