I went with Jackie Brown though I like Reservoir Dogs a lot too.
I think Pulp Fiction is the most eminently watchable and rewatchable of all his movies. The fact that it's kind of three movies kind of hurts my opinion of it. Having said that I think I personally like the tone and execution of Reservoir Dogs above all of them so that's my vote. I still need to see Django Unchained toot sweet. Love all his movies regardless of corniness.
inglorious basterds is whole-heartedly my favorite for reasons i cannot explain, i'll re-watch it at least once a fortnight. though it is not his best (that award goes to pulp fiction).
django unchained, (which i only viewed two days ago) appears to be his best work since pulp fiction. the scene with the 'skull and the dimples' had me holding back laughter at how 'typical tarantino' it was, i've always loved tarantino's style of unnecessary build up before chaos.
Jackie Brown is the best. Its the only movie with a real heart. Followed by Reservoir Dogs and then Pulp Fiction. Remember seeing Reservoir Dogs at the cinema and being amazed at the time though. Crazy how much of a fuss all the violence caused when you think of all the stuff which comes out these days.
I don't really think he has made a properly good film since JB.(I haven't seen Death Wish or Inglorious Basterds) Kill BIll is awful and overlong, the worst film of his I have seen. I wish he would stop trying to ape all the movies he remembers as a kid and make something really original. I can't cope with all the nods and winks in his current work.
I'm going to have to say I love all of them, but I think Pulp Fiction may be his best work, when you look at it in context. Also you don't have My Best Friend's Birthday on there! I know it may not count, but come on, you should throw it on there for laughs.
I've only seen his movies of this millennium, but I'd probably put Kill Bill Vol. 2 at the top, followed by Vol. 1, Inglourious Basterds and Django.
I absolutely adore the tributary and just insane style of the Kill Bill movies, and I think Inglourious Basterds has perhaps the greatest ending action sequence of anything ever. I quite liked Django (Christoph Waltz is pretty amazing in it), but I just feel like the last half hour was slightly pointless.