X-Men: The Last Stand (aka X-Men 3) went through a lot of changes before production began, including a hunt for a director that included a pretty extensive list. The 2006 installment in the X-Men franchise was a financial success, but received mixed reviews from critics and fans. Co-writer Simon Kinberg, who went on to write and direct X-Men: Dark Phoenix, even publicly admitted that he wanted to use the latter movie as a way to correct mistakes made in X-Men: The Last Stand.
Directorial duties were handed to Brett Ratner after several other directors left the project. Ratner had been considered to helm the first X-Men film years earlier, a movie that went through an even longer development stage, before it was offered to Alita: Battle Angel director Robert Rodriguez, who eventually turned it down, opening the door for Bryan Singer to take over. By the time Ratner was on board for X-Men: The Last Stand, there was less than a year between the start of filming and its announced release date. Many faults with the movie can be blamed on the short production time on such a large scale project, plus possible tension on the set due to inappropriate behavior by Ratner, who has since been accused of sexual misconduct.
While Ratner was the final choice for director, there were quite a few before him. Several people were rumored to be up for consideration, a few turned it down, and there was more than one who were actually attached and did some pre-production work. The list begins with the director of the first two installments of the franchise: Bryan Singer. Singer, who has also been accused of sexual misconduct, began work on the third film in the franchise after completing X-Men and X2: X-Men United, but decided to leave the project as he was more focused on bringing Superman Returns to the big screen. He took the original screenwriters, the composer, and star James Marsden with him. Development continued with new writers and Matthew Vaughn, director of The King's Man, eventually signed on for the movie, even casting some of the major roles, but was forced to leave the project just weeks before filming began. Between the time Singer and Vaughn worked on the movie, there were even more directors discussed.
Hugh Jackman reportedly wanted The Fountain director Darren Aronofsky, but it didn't work out. The two almost collaborated again on The Wolverine before Aronofsky bowed out before filming began. It was reported that Joss Whedon was offered the chance to direct X-Men: The Last Stand, but he was instead focused on Wonder Woman (which of course never happened). Other directors in the mix were Rob Bowman (Elektra), Alex Proyas (I, Robot) and Peter Berg (Battleship), with the latter two said to have turned it down. Justice League and Watchmen director Zack Snyder was also on the list, but his adaptation of 300, which released the same year, meant he was too busy. It was reported that A Good Day to Die Hard's John Moore was under consideration right around the same time Ratner was finally chosen as well.
All of these directors would have presented a different version of X-Men: The Last Stand. It also would have come down to prep time and meeting a schedule presented to the studio. Matthew Vaughn was concerned that he wouldn't be able to properly make the film he would have liked with such a short turnaround time. He did, however, get another chance to work with the X-Men with X-Men: First Class a few years later. The future of the X-Men remains in flux with Disney now owning them and having to decide if and how to integrate them in the Marvel Cinematic Universe, though it remains to be seen whether any of these directors will get the same chance again.