X-Men: Days of Future Past

Essential, and this is the film that breaks the timeline on purpose, which is the single most important fact about watching this franchise. A consciousness is sent back from a ruined future to 1973 to prevent an assassination, succeeds, and the series' history is overwritten from that point forward. The Last Stand's ending is deleted. Characters killed in earlier films are alive in the last scene. Origins never happened.

That is why the hub recommends release order: watched in sequence, you see a franchise edit its own past in public, which is a genuinely interesting thing to witness. Watched in chronological order, the cause arrives detached from the effect and several earlier films describe events that no longer occurred.

The film itself is the best-constructed in the run. It has two casts, two time periods and a ticking clock in each, and it manages all of it without losing the thread. The 1973 material, with a Nixon-era Pentagon, a paralysed and addicted Charles and a Paris peace conference, is the strongest; the future sequences are a slaughter with no survivors and real weight.

The Quicksilver kitchen sequence is the most purely delightful two minutes in any of these films. A longer Rogue Cut restores about seventeen minutes and a subplot; it is more complete and slightly slacker. Watch it after The Last Stand, which is the order in which the repair makes sense.