If you're going to use a UV filter, use a good quality filter.
While a casual look would be difficult to tell the difference between a poor filter vs. a good filter, I took a shot to illustrate the difference in a way that makes it a bit easier to notice the difference.
A high quality filter will have good anti-reflective coatings -- almost completely eliminating reflections. Reflections are bad for 2 reasons...
First, the only way it can be possible for you to see a reflection is if some percentage of light striking the surface of the filter is reflected back. That means not all the light is actually going through the filter.
But the second reason is that light that does make it through the filter on the first pass can reflect off the front of your lens and back onto the filter a second time. If the filter doesn't have good antireflective coatings, then some of that light will bounce back again and you'll get "ghosting" in your image (caused by reflections.) And these can be very annoying.
To show this, I took a piece of black poster-board (card stock from the local craft store) and cut it into this strip.
I placed two filters on the card stock. On the desk (out of frame) there is a lamp providing the light. I lined up the filters so that the light source is between the two filters.
Notice, however, that when you look through the filter on the right, the card stock is nearly as black under that filter as it is in the area where there isn't any filter at all. It almost looks as though I've placed a ring on the card stock that doesn't have ay glass in it (there is glass in it - but that's a filter with high quality anti-reflective coatings.)
Meanwhile the filter on the left is noticeably lighter. The card stock looks a bit washed out through this filter. We are getting an overall reflection which is causing a bit of a loss in contrast through that filter.
I can tell you (because I own both filters) that if I hold the filter and tilt them in my hand to treat them "like a mirror" that the reflection in the B+W brand filter on the right is there... it's just weak. It doesn't create a very strong reflection. Meanwhile the filter on the left does create a much stronger reflection (it either lacks anti-reflective coatings entirely... or they're just not very good anti-reflective coatings.)
If you're gong to put glass in front of your "glass" (particularly if you invest in expensive high-quality lenses) then you'll want to match that with a high quality filter.
I own filters for every lens in my kit. But most of the time I don't use them (my lenses are 'naked'). But "just in case" I want to shoot in an area where where the environment isn't as friendly to the lens, I have the filters with me.
I also typically have a Circular Polarizing (CPL) filter as well as a 3-stop Neutral Density filter (ND 0.9).
I've gravitated toward B+W brand filters because of their repuation for very high quality and my ability to notice that it does actually make a difference. I do not happen to own Hoya Pro1 series filters, but they're also generally regarded as good quality filters (only the "Pro1" series - Hoya makes other filter series but they're not as good.)
