It depends for what lens you intend to use. If it is a very expensive and excellent
lens you may want a filter that can be all that. If not does it make a difference?
I use a relatively cheap Hoya one, paid ~$45 for it (for a 58mm one). I'm perfectly happy with it. No flare problems as it is coated, and you can really see the difference with blue skies and reflections from glass and glossy paintwork.
I don't know how whether there's much difference. Frankly, when I bought my 24-105mm lens, I asked the camera store clerk for a polarizing filter to match. He suggested a Marumi DHG circular polarizer. It seems fine, but I admit I've never considered comparisons. (Just Googled, it's available in 77mm for less than US$50 on Ebay.) For previous polarizers I mostly bought Hoya.
To all who responded, thanks for the information - I've bought Hoya and Tiffen filters over the years, never could tell any difference.
Given changes in technology, didn't know if there are any discernible differences now, other than the prestige of a 'designer' filter. Too, I've read reports attributing calamitous results to light bouncing back-and-forth between the sensor and rear side of the filter - any filter- causing faulty exposures...don't think I've reached that level of OCD yet
