Yeah the whole genre system in IMDB is pretty "vague", it gives you all the closest genres and sub-genres to classify a movie.
That said, while some dont consider movies like "Heat" , "Memento" , "Bullitt" or "Serpico" as pure Neo-Noir - they certainly contain Noir elements one cant deny.
But given all the possible choices, I agree about Chinatown - the best of the lot.
2nd Greatest Neo-Noir/Post Noir : "The Manchurian Candidate" (1962)
3rd greatest: "Fargo" (1996)
P.S - Have u seen the sequel to Chinatown - "The Two Jakes"?
did u like it?
"Come out and take it, you dirty, yellow-bellied rat, or I'll give it to you through the door!"