I find the OM-1 smoother and quieter than the OM-1N. I have 5 OM-1's and 2 OM-1N's to compare.
I like the OM-1 because it is more pure in appearance, especially around the eyepiece and hot shoe mounting area. (but that's just my obsessive compulsion order showing)
One other thing. The Black OM-1 has an all-black meter switch and the Black OM-1N has a white stripe in the switch which I find annoying. (compulsion...)