I usually use a UV filter to protect the front lens element from dust, scratches etc. And it can assist get rid of UV light that may degrade images but I try not to obsess. When I have bought new DSLR lenses my local camera guy trys to sell me very expensive "designed for digital", ultra thin, multi coated filters that cost a small fortune. I usually resist, figuring its an unnecessary expense.
When I have succumbed and been seduced into making the purchase I cannot say I have seen much if any difference. But I dont like the idea of the front elements of my lenses being naked so I will use some kind of filter - often a Hoya, sometimes a B&W or Marumi- it depends on what has a reasonable price and is available.
I do like filter rings to match the lens - so if its a chrome lens, other things being equal I like to use a chrome filter if I can (its not always possible). So this is a consideration for many of us too!
Of course with my M8 an IR cut filter does help so I usually use one as a matter of course.