yahoo was better few years ago, but bing competing well too. they got map , videos and images. all quality get better than yahoo. i will say still both are same.
While Google will likely always be a leader in PPC advertising, we often recommend Yahoo and Bing to our clients in order to get a higher click through rate on their ads. Because the Yahoo/Bing markets aren't as saturated, people may be more likely to click on your ads (when they are relevant). The only downfall is that you probably won't have as many impressions, since Google is a more popular search engine.