There are actually a number of factors that go into which you might trigger the most, our primary source is Yahoo! but we also pull from Bing and Yandex in certain regions, as well as information from 400 other sources including Wikipedia, and our own crawler. You can read more about the sources here: https://duck.co/help/results/sources

We try and provide the best results for a query in a region/language regardless of the price. The only caveat is that we will only pull from sources that allow us to continue our privacy commitment to users.