Do you mean their Ad system? Actually google has recorded the market trends like no one did before. Even, there are lots of news articles, marketing share reviews etc which will let us know about the approx. stats of their ad system/market shares. And of course yahoo doesn't have huge ad publisher network like google have around the world.
There are certain features that Yahoo have which can be differ in Google. You can't compare both of them because it has different features that netizens enjoyed it.
Google is the best and Yahoo no longer accepts add url from their own. They are now sharing data from Bing.
Google and Yahoo are both huge internet companies which compete in a lot of areas, including free webmail service. When Gmail was launched back in 2004, lots of people moved to Google's new, convenient email platform. Yahoo! answered by redesigning their own e-mail system and offering more space and features than they did before.
For SEO, Google is better than Yahoo. Yahoo has different features which ae very good like mail, yahoo neqws etc.