Ross has done really hard work in making a sticky post and presenting total picture on getting traffic at one place. Reading the post again and again refreshes information and reminds you if you skip certain source.
Basically all the sources are good. It all depends how expert you are doing certain things and how you exploit a particular source say for example a forum or article directories or blogging. Trust me, switching back and forth to 3-4 sources and promoting consistently for a long period brings good results.