I need to put my post-based rank on a higher level and this topic is very interresting, so let me explain my opinion on this matter:
I have seen all of the QT-Movies in the cinema and at home, dubbed and undubbed, and all of them are quite entertaining. Yet the first three movies are masterpieces and the last four ones are just "very entertaining".
I put it into figures:
Reservoir Dogs: 10/10
Pulp Fiction: 10/10
Jackie Brown: 10/10
Kill Bill 1: 8/10
Kill Bill 2: 7/10 (cos of the 2nd half)
Death Proof: 8/10
Inglorious Basterds: 8/10
I do think the first three movies developed his own "style". Any quotations of Spaghetti-Westerns (Reservoir Dogs) or Blaxplotation (Jackie Brown) were subtle. With the last movies he tried to make "genre-films" and did not stick to his developed style of gangsterfilms. The copy of Morricone musik in Kill Bill and Basterds was to obvious and just told me that he is a big fan of westerns. In addition to that, the actors in the first three movies are better than the actors in the last 4 movies: Harvey Keitel, S. L. Jackson, Travolta, Pam Grier, de Niro and so on.
I think Pulp Fiction will ever be his greatest film.