Google Or Yahooo
Well, every search engine has its own method of searching, indexing and returning results to user-queries, and no one can actually compare between different search providers..
However, Google is a more popular search engine and as it focuses mainly on search, we can presume that it does that work quite well. From my personal experiences, i can tell that a search query in Google returns more important results than other search engines. this is because Google has employed a considerable amount of research time into evolving the most efficient technologies for an efficient and useful search engine.