As a lot of answers here it depends. What is the product or service your offering? Is it I need you now? If so AdWords is way better than FB. Example I lost my car keys. The customers not going to search fb for a locksmith the 1st place there going is google. On the other hand and your a restaurant that has a bitching offer that would work better on fb. If your a locksmith offering a get a car key get 2nd at 50% off that could go either way. Hope that clears things up a bit