Release order is best for first-time viewers. Chronological order is a trap that ruins the storytelling. The MCU was deliberately structured so that watching in release order reveals plot twists, character arcs, and thematic depth that chronological viewing spoils outright.
The filmmakers built narrative tension across films. Captain America: The First Avenger (2011 release) happens in 1945, but watching it first ruins setup from Iron Man, Thor, and The Avengers that came before it. Avengers: Endgame has massive emotional payoff that only lands if you have seen the character journeys unfold in release order. Chronological viewing flattens these arcs and feels scattered.
Only for rewatches after you have seen everything in release order. Even then, it fragments the experience. The one exception: Captain America: The First Avenger can be watched right after Thor without spoiling much, but do not do a full chronological rewatch on your first go.
The Netflix series (Daredevil, Jessica Jones, Luke Cage, Iron Fist, The Defenders) fit loosely into the timeline but are not essential. Agents of S.H.I.E.L.D. is similarly optional. Disney+ shows (WandaVision, Loki, The Falcon and the Winter Soldier) have more direct movie ties and are worth watching, but the movies stand alone.
Pro tip: After Endgame, the MCU becomes more fragmented. The newer films feel less interconnected — watch them as they release, but do not sweat the order. The Multiverse has given the writers an out for continuity.