"No one ever got fired for telling clients to advertise on Facebook." That's the sarcastic mantra making its way round the digital advertising world right now. But is Facebook actually an efficient vehicle for marketers compared to the other digital ad giant, Google?

A comparison of the two companies from WordStream, a search marketing management company, suggests that Facebook is a much less effective ad medium than Google. (The caveat here is that WordStream is, obviously, rather more dependent on Google than Facebook as a medium.)