Actually Yahoo and Bing are closely the same since a while back, http://mashable.com/2010/08/24/bing-powers-yahoo-search/#W2g2NCa40gqH
I have not used Yahoo in years. I think I even stopped using it before this post was made, lol. My suggestion is to always use Google. It is #1 for a reason.
However the thread is about Yahoo being the worst, not about what is the best. Either way, there are only two search engines to choose from; Google and Bing, so not much left to opine. Nonetheless Yahoo is not longer a search engine at all, hence why it's so bad; it's being receiving "second-hand" result from Bing, which powers all searches performed on Yahoo.
To an extent it's right. Yahoo indexs very slow and my site is refreshing very well while he really downgraded and while I keep it remian for long year, my keywords listing on top page, it doesn't make any sense.
Actually, I am always using Google Search Engine. Although I am used Yahoo Search, But I think Google search is a better search engine. And it's more user-friendly than any other search engine.