All time, probably the Cinesphere at Ontario place — one of the very first IMAX screens ever built, inside a geodesic sphere.
Currently (and closer to home) the IMAX theatre at our local museum. They show all sorts of IMAX formatted films (they have a full 4K Laser IMAX projection system), and their snack bar is hard to beat: excellent popcorn and hot dogs, lots of snack options, and the prices for which don’t break the bank (especially when compared to all the other theatres in our area). Last time I went (to see Oppenheimer) I got a large popcorn, large Coke, and a cup of gummy treats — and I think I spent a whole $12 (CAD).
And while I don’t have one, they have an annual pass available.
I know you weren’t directly questioning my assertion, but in case anyone else happens to think I’m just blowing smoke: Coloured Fuel | DriveSmart BC.