http://ero-advertising.com is the best paying xxx ad network in 2013. I checked all of the companies on my websites, and I've been making the most money with them. They also pay in Euros instead of Dollars, which are worth more (0.76 Euro = 1 Dollar). So it is 20% more income, and the currency value.
One of the things is, that the popunders open more often, I think.