As far as Facebook advertising goes against other advertising, like AdSense or another system, it's the most targeted, and thus the best.
I have a background in tech, and I've helped people spend untold thousands upon thousands of dollars in internet advertising. The main issue is how to target the people you want to target.
It's the same way that you can get very targeted mailing lists, down to specific areas. Places like Google can target a perceived specific group of people based on the content of a web page. If you invest in real estate keywords, your ads will show up on places that have those words or related content, the same way that searches are ranked.
However, you are still only guessing. You can't actually know that the people you are advertising to are X-Y age, Z gender, and so on. At most, you are approximating.
With Facebook, however, you know exactly who these people are, because they have volunteered that information. You can target people who are 25-35 because Facebook knows everyone's birthday. You can target men because they know their age.
You can target people who listen to a certain kind of music, people who have "real estate" listed as a job or an interest, who are involved in real estate Facebook pages, and so on.
There is so much information that we provide to Facebook that it's almost scary, but that is what makes advertising with them such a lucrative business. There are half a billion people who have volunteered such an incredible amount of personal information that the advertising that goes on will be the most successful possible advertising you can get on the web.
That being said, there are also high-traffic sites that, instead of using something like Google AdSense, do deals directly with people who want to advertise. These are also lucrative resources, but you end up paying a good amount more.