There are many ways to judge this, so it's important to clarify the question. Fame and popularity are thus more important in this case than critical Sherlockian opinion.
Quotations can go in and out of style.
By considering public opinion at many points in time, we can determine the most quotable stories of all time. Judging public opinion is a subjective process. Fortunately, we can look to general quotation experts for guidance. Our sources then are the editions of Familiar Quotations by John Bartlett or The Oxford Dictionary of Quotations that contain passages from the Sherlock Holmes stories. They provide data for the period from 1891 to 1992 and are the acknowledged leaders in their field.