Bing now runs yahoo search and facebooks mail as well as owning Skype. Slowly they are taking all of Yahoo's unworkable parts.
I am not sure, what you want to tell actually. Your thread's title is about yahoo popularity and later asking about Google and Bing! If you tell about Popular search engine then it might be Google.
We all know that Google is today's best search engine. It produces the greatest part of the overall traffic on the Web. Webmasters value good PageRank in Google much more than showing in other less distinguished search engines. Google is constantly gaining more and more popularity. Almost all people use Google to search for quality content on the internet