When you are saying best gunplay scene ever, for me it has to be the intense bank robbery shoot-out in Michael Mann's 'Heat' (1995) (
oh no, I've mentioned a US movie for the best shoot out, thats gonna really tick the fanboys off, lol). I liked this scene very much as it uses gritty, NYPD Blue/documentary style handheld shots to emphasize realism and the sound effects are very high in impact (as with all of Mann's films).
My favourite shootout in a Hong Kong movie is still the teahouse scene in 'A Better Tomorrow', the camerawork, editing, sound and the cool charisma of Chow Yun-Fat executing almost everyone who was in the room with his trademark 2 colt .45 pistols and the long black overcoat. Classic, although I do enjoy the church shootout in The Killer, the shootout at the Saigon nightclub in Bullet in the Head and the (bald) head-to-head face-off between Tony Leung Chiu Wai and Lau Ching Wan in The Longest Nite, it was very dark and intense.