For me, it has to be, Pulp Fiction. I love the use of cross-cutting to explore the storyline, and Tarentino's dialogue is second to none, I can't think of any other film with as many recognisable quotes.
"you know what they call a quarter pounder with cheese in paris?"
"they don't call it a quarter pounder with cheese?"
"No they got the metric system over there they wouldn't know what the f**k a quarter pounder is!"
"Then what do they call it?"
"They call it: A Royale with cheese"
"A Royale with cheese!"
I don't know, for me the best Tarantino has got to be Jackie Brown.