Two brilliant choices. Jackie Brown is one the most underrated films of Tarantino, people complain sometimes about the stylistic, unmemorable and masculine/immature nature of some of his characters such as Jules and Vincent (who I love) then in Jackie Brown he goes and gives us two characters who give fantastic performances and both have characters who I love to watch on screen and people still complain, probably because one is a woman and the other an old man. Robert Forster is brilliant in a great film.
I am a massive Steve Buscemi fan and love most of the stuff he's in, all the dogs are great but Mr. Pink appeals to me I think because he is a more innocent (perhaps), smaller (in size, as opposed to the bigger/stronger guys) yet he tries to hold the situation together well and ultimately comes out on top. I think I'd have Mr. Blonde ahead of him although both very close.
Can't wait to see your final three, this list just reminds me how many great characters Tarantino has created without the amount that are gonna miss out
EDIT: My bad just seen you already posted #3, but great choice with Butch. Bruce is perfectly cast in
Pulp Fiction and his watch chapter is one of my favourite parts in the film, love it when he gets back to Fabian with Zed's bike, "Zed's dead baby, Zed's dead".
Also, for the record, Jackie Brown is in my top 4 Tarantino films, although I love all of them and would rank them very closely (as you will have (and will) see in my list),
Death Proof is his weakest film but I still loved that and would give it
+, the first half of that is as good as any he's done, and whilst I doubt Stuntman Mike will make it in to the top two, he's also a fantastic character portrayed by the perfectly cast Kurt Russell.