Honestly, I think Google. I don't think Facebook is very effective for advertising. People go to google in order to search and or buy products. They tend to go to Facebook to chat and view friend's profiles...just my opinion.
Google is a search engine, so advertising works best there, where as Facebook as a social media platform helps to interact with customers, It lets you know the need of the market. Using them simultaneously, can produce good results
Google and Facebook currently provide two entirely services with two different business models. However, you can see a potential future where the two business collide over mobile search and the monetisation of social media.