I use Hoya filters exclusively (price+quality) and have a full set of the UV Pro multicoated for each of the lenses. I don't care what people say about that. I'm not spending 1700 on an L lens just to scratch the MFer by being an ass in the field and dropping, scraping, etc., my dear, dear didn't eat for a month lenses.
And check this bit of technical information out. If you REALLY think you are getting a better picture with the UV filter off, you can u-n-s-c-r-e-w it in the field. I've done this numerous times while stacking/unstacking for variable light instances.
I can't tell any image degradation with or without, but I use the Hoya multicoated filters too. Multicoated filters are a necessary condition to avoid aberration or fringing also.
Last, you can't go wrong with Hoya. They are quality.