I typically buy coated filters, but I have also used non-coated filters and been happy with the result.

I usually don't get too worried about image degradation. Actually, the entire reason I am using filters in the first place IS to effect the image. I never use a filter to protect the lens, instead I want the color adjustment or the polarizing effect. If not, I see no reason to use it. So, as long as the filter glass is quality glass to start with, I figure I am getting what I want.