Jean V?ronis with the help of his students has done a Search Engine relevancy test. The test was done as follows:

Fourteen topics were selected in order to reflect a broad variety of uses (Animals, Cinema, Current Affairs, etc). Each topic was attributed to a different student, who was then free to choose five search queries. The format (with or without quotation marks, one word or several words) was also entirely up to the student. The study was intended to be a ?blind test?, with users not knowing which search engines provided the results, so I entered the 70 search terms into the six search engines myself. The first page of 10 results not marked as sponsored was archived for each request and each engine (4200 results in total), then automatically stripped of all information other than the resulting URLs.

And the winners are Google and Yahoo!. Read the full article here