This is a very common question and one that does not have a clear answer. Pro photographers have pretty much confirmed that there is no real advantage when it comes to the affect on the quality of images. With digital cameras now getting smarter and better equipped the problems caused by UV light have been overcome.
The one area where it is agreed that UV filters have a good use is for protection.
Adding a UV filter to the end of a hard earned expensive lens makes a lot of sense. This will help prevent excessive dust and will scratch proof the lens.
The best option is to go for a decent quality filter and to keep this on at all times. There is no point going for a cheap filter on an expensive lens!