I had a lot of UV filters, 1 for each lens a while ago, and they were all decent makes, mainly Hoya but they still degraded the IQ of the lenses too much. With my first 7D the IQ was so soft I was on the point of returning the camera until I shot some photos without a filter and the difference was so noticeable I removed all the filters that day.
I have a Hoya Pro1 CPL and a Kenko CPL that get used occasionally and they don't seem to degrade the IQ anywhere as much as the UV filters did. The only time I use UV filters now is if it's going to be excessively dusty or wet weather although it's been nearly a year since I've used them.