Moldvay and Cook B/X or Old-School Essentials are going to be some of the fastest, if not the fastest around. Each other edition of D&D adds boatloads of complexity to the characters and piles of hit points, which adds time to resolving combat. With the exception of 5E, which is faster to resolve than 3X or 4E, but no where near as fast as 1E or 2E...or B/X.My least favorite thing about D&D is waiting half an hour for my turn to come around in combat.
So which flavor/branch of D&D has the quickest combat, in your experience? I assume it's some varierty of OSR, but please enlighten me.