Yahoo and Bing can do well, yes. I mean my point was this.
Adwords is thr largest Ad Network around, it is also a majority search related traffic, Facebook is the largest Social Network around, the Ads are served in Users news feeds based on FBs algos and what you choose via interest targeting.
You can bank on either if you know how to Track, create quality Ad sets, create quality landing pages with Copy that will convert a user to a sale, Trial, or lead.
There is other things to this, but the point is you asked which is better, I was saying Adwords traffic is more targeted, but bother are great