I would recommend 2.40:1. Most movies coming out in widescreen format are either 2.39:1 or 2.40:1. If you go 2.35 then you will have slight black bars on the top and bottom of the image but if you go 2.40:1 a 2.35:1 movie would only have slight black bars on the sides. Slight black bars on the side of the image are less distracting in my opinion since they are closer to your peripheral vision area.
You could zoom if you have a nice black velvet border of course but I am extremely happy with my 2.40:1 after owning a 2.37:1 screen in the past... just food for thought
Why not slightly increase the size of the image, until it fills your height? The tiny bit of information that you lose on the right and left is not going to have anything critical in it. Using a 2.35 gives you a slightly bigger 16:9 image.Excellent advice. I presently suffer with a 2.35 screen watching 2.40 movies.