Both are very good search engines, and have different algorithms which are very good at helping you locate informations. But i prefer Google because of it's simplicity. When I'm doing a search, I prefer not to have to wait until all of the news stories come up. Google has it's nice simple into page with no extraneous stuff to get in my way. However, Yahoo does have the news items and personal interest items. It all really depends on how urgent my search is.
of Course Google and Google is not made for best in Search Engine it is also the best in all features then Yahoo.