[Pils]

It's widely known that Facebook is worse than Google in terms of conversions. People go to search engines to find something, people go on to Facebook to browse Facebook. What Facebook offers over Adwords is fine-tuned demographic targeting. So it's good for brand awareness (think traditional TV ads) and products that require targeting very specific demographics where the few conversions are highly valuable(new CS grad hiring, women on dating websites).

[shostack]

It very much depends on your goal. Many advertisers, myself included would say "it depends on your goal." Search has some major limitations over paid social for things like branding campaigns. Even for direct response it is hardly black and white. I have FB campaigns that have performed better than some search campaigns.