I use high-grade, multi-coated, clear, NON-UV protection filters on all my better lnses.
Hoya HD or Pro1 Digital Protector or B&W 007 clear MRC.
I avoid UV-filters, they are unnecessary and may degrade image quality slightly. The cheap ones will for sure.
I take my hi-grade protection filters only ever off the lens, when I use another filter - circular pol filter, ND or ND grad.
I also take them off in dark conditions wehn tehre are point-light sources in the frame - that's the only time I ever saw a possible negative effect on image quality ... reflections / ghosting. If you pay attention, you will see it in the viewfinder and take the filter off in good time.
I am amazed how much drig and dirt regularly accumulates on the front of these filters, although I treat my lenses rather well. Air in our cities is not as clean as you would like tit to be .. is all I am saying. Not even to mention really harsh environments with mist, spray, beaches or on the tarmac of an airport next to a 747 being de-iced with huge amounts of orange de-icing agent ... with a good filter .. you just wipe it off. Way easier to clean than lens front elements.
But .. your mileage will vary ... if you never leave the clean room, you won't need protetcive filters. :-)