Tricky question... I admit I loved Pulp Fiction for a loooong time. But for now my favourite is Django Unchained. Surely the best of Tarantino in a movie. Then comes Inglorious Basterds, then Hateful Eight and then Kill Bill Volume 1 and 2. Though it'as hard to have a true favourite. Tarantino loves to make movies that are really different.
Defiinitely Pulp Fiction for me. One of my all time favourites; I don't think he'll ever top that movie. Anyway I enjoyed every Tarantino Movie that has been released since Reservoir Dogs