IMAX 70 is good, but supposedly laser projection IMAX to is better. Availability of regular IMX and laser projection IMAX theaters can be found here. (Sadly none in NY or NJ)
http://ew.com/movies/2017/07/19/dunkirk-imax-70-mm-where-to-see/
"Some theaters are also showing the movie in IMAX with laser projection. This means a laser light force is used instead of a standard lamp, which broadens the color palette (blacks look darker, for instance), amplifies contrast for highlights and shadows, and brightens the image."
(Steve, only place in CA is Grauman's Chinese Theater in Hollywood where I saw Star Wars in 1977 two weeks after it opened and literally fell out of my seat with the opening scene.. I'll never ever forget it.)
but Imax Laser is digital 1.43, not film.