WordStream notes that Google also offers twice as many ad formats as does Facebook, including in-video ads. Google also offers mobile game ads, while Facebook does not yet support mobile advertising at all.

"So far, Facebook's advertising platform hasn't kept pace with the explosive growth of its social network, and it remains to be seen if CEO Mark Zuckerberg even wants to focus on advertising as a source of revenue," Found and CTO of WordStream Larry Kim said in a statement. "In [Zuckerberg's] 2500+ word letter to shareholders this month, he mentioned advertising just once."

Shopping for Friends vs. Searching for Car Deals

Tech company founder and investor Chris Dixon notes, , that while Facebook has a "lot of room to target ads more effectively," presumably by utilizing the , ads work "dramatically better" when people have purchasing intent.

In other words, Google's ads work just a little bit better because Google is a search engine--people often use it to search for products and prices. Facebook, on the other hand, is a social network, and most people are not using it to shop around for the best deal.