LensRentals.com - Good Times with Bad Filters. Is a great example of how filters affect image quality. Most folks I know don't put a filter on top of the lense. I put them on all of mine because one scratch and your $$$s lense is well not so nice.
In terms of brands, I've been using B+W (very, very expensive) and not Heliopan (even more expensive). But fredmiranda.com points out there is a review of UV filters. Normally you put a UV filter on as protection from http://www.lenstip.com which does a review of UV filters. I had not seen that before and surprisingly they like the Hoya filters which is a huge surprise they absolutely disliked the Tiffen product.
They apparently don't make the UV-0 series anymore though. And from the chart you can see there is definitely a difference between the more expensive pro filters and their other lines. At the time of this review, they were the Hoya UV-o and the B+W MRC.
Today, the latest versions are the Hoya HD and the B+W XS-Pro and stackexchange.com that they are both great with the only issue being Hoya uses aluminum whereas B-W uses brass says. And dpreview.com explains the new HD2 carries a longer warranty. It is UV and Protector filters are lifetime and others are five year.
|1||Hoya 72 mm HMC UV-0|
|Hoya 72 mm Pro1 Digital MC UV-0|
|2||Hoya 72 mm HMC Super UV-0|
|3||B+W 72 mm 010M UV-Haze MRC|
|4||Hama 72 mm UV HTMC 390 (0-Haze)|
|5||B+W 72 mm 010M UV-Haze MRC Slim|
|Marumi 72 mm MC UV|
|6||Sigma 72 mm DG UV|
|*||Kenko 67 mm Pro1 Digital|
|7||Heliopan ES 72 mm UV-0 SH-PMC|
|8||Marumi 77 mm WPC UV|
|9||Hoya 72 mm UV-0 - Standard|
|10||Hama 72 mm UV 390 (0-Haze)|
|11||B+W 72 mm 010 UV-Haze|
|B+W 72 mm 010 UV-Haze Slim|
|12||Heliopan ES 72 mm UV-0|
|13||Marumi 72 mm UV|
|14||Hoya 72 mm UV G - Series|
|15||King 72 mm UV|
|16||Tiffen 72 mm UV|