I own both Hoya and Tiffen circular polarizers. I cannot tell a difference, but perhaps I haven't taken a shot in just the right circumstances to prove ones flare over the other. I think Tiffen makes a "decent" product, but if you can swing it, get a better one in my opinion. (one less thing to worry about)
Also, if you are thinking about other lenses in your future, look them up online and see what size filter they require.
Example: Say you have your heart set on a Sigma 50-500 lens. Thats an 86 mm filter. I would buy an 86mm polarizer and a step up ring 67 to 86mm. Step up rings are cheap, filters are not. Just a thought to help save you some money down the road.
Derrick
Another thought, I have bought 2 Tiffen filter kits in the past. Although I am sure many will disagree with doing this, they were an invaluable learning tool for me. You get 3 filters- a circular polarizer (i found nothing wrong with the 2 I got), a warming filter ( i did have problems with one of mine, Tiffen laminates the color between 2 pieces of glass and mine had trapped air bubbles. I likely could have got a replacement, but never tried), and you get a UV filter-good for lens protection. 3 filters and a filter case for a reasonable amount. Just another thought. Sometimes you have to avoid the internet and everyones opinions and take a leap and try things and have fun, unfortuneatly things aren't always going to go in your favor. What I mean is, I read these darn forums so much that I start worrying about shutter life and how many more shots my 6 month old camera has. LOL