We know that the best search engine can reply to us as many result as we wish. And I believe this three search engine occupy good algorithm to produce the searching result, of course they are supported by many good programmer to make them the best search engine.
But in my point of view, Google the top one, since it can reply you more result than the Two (Yahoo or Bing), because I saw that Google is very concerning in its motto to become the best search engine. This was saw from when it's born at the first time. This is not happening to Yahoo and Bing, since there are become less popular nowadays.