The view I've seen chucked round a lot is that social ads (i.e. Facebook) are much more effective than almost anything except a Google ad that is on a Google search results page. This is especially the case if you're trying to build awareness of a product a viewer would have no reason to otherwise search for in the first place.
This point is likely to prove very contentious thanks to a critical mass of HNers with vested interest on either side.
Agreed; social ads are just a more refined version of banner ads. You can push ads at your target demographic until the cows come home, but ultimately the effectiveness of that strategy will be upper bounded by that of sending Shutterfly link to somebody who just Googled "photo prints". Anecdotally, the only ads I have ever clicked and not regretted it were served up by Google.
The ads I clicked and actually found a lot of value in were for small speciality stores on small specialized websites. The thing is, I never see most ads because I run ghostery and https everywhere (no adblock necessary, not sure which of the two does the job though). The ones I see are mostly the useful ones not served by a network.
This point is likely to prove very contentious thanks to a critical mass of HNers with vested interest on either side.