Romeo and Juliet may be Shakespeare's most well-known play. It is probably not his best play, but it's a good one, and a lot of people have a vague idea what it is about (but not, of course, how it ends). Hamlet may possibly be his most famous play as well, since it contains the one Shakespearean quotation which everybody knows. Unfortunately there is no reliable objective way to measure fame, so we are stuck with speculation.