Here is my take on filters, take it for what its worth.
I do not use them on lenses that can be taken off the camera. So DSLR, I do not use them, video cameras that do not have removable lenses I do.
Here is why I feel that way.
Obviously a video camera lens issue results in a non working camera.
For dslr users if its your only lens, maybe you should use them but if you have other lenses why put another piece of glass between you and the subject.
If your afraid of a scratch, it would take a pretty serious scratch to degrade the image, and it s not like it would ruin your lens, they can be sent to Canon to be removed.
Lenses like the 400 2.8L IS have a built in filter, in other words the outer glass is for protection and from what I am told the lens works perfect with out it. (someone on sportsshooters had it fall out) This makes me wonder if other lenses have the same thing, an outer protective glass.
I just always use the lens shades, keeps fingers away, offers some protection and no effect on the image.
Back when I did use filters I uses Hoya and not sure how, but still had dust get in between the filter and the lens, so I would have dust on the outside, and inside and felt that could not help image quality.