I have substantial experience with Polk products both as an end user and I sold it as well back in '99 - '01 and can offer some advice....
Polk Audio is a good brand of speaker with a lot of die hard fans and happy owners all over the world. They used to be real big with the small shop & custom retailers, but fell out of favor with a lot of dealers when they went into the big box shop CC. Since you didn't mention what type of Polk speaker you are looking into purchasing, I will detail my thoughts on their entire line.
Their box (towers & book shelves) speakers are by far their best product. Classic looking speakers with great build quality. Polk's are a very true sounding product, but don't expect them to blow you away. I mean that in a positive sense. Meaning they aren't designed to add flavor or color one way or another into your source material. No crazy bass or bright highs here at all.
A $500 speaker from Polk sounds like a $500 speaker, a $200 speaker from Polk sounds like a $200 speaker, etc. You get what you pay for. I haven't checked recently, but they used to one of the only cost conscious manufacturers that still made their speaker boxes out of real wood. That could be changing since they were recently acquired by Def Tech's parent company, Directed Electronics. Matthew Polk, the company's founder is staying on to run the brand though, so look for some things to stay the same.
I personally feel that Polk subwoofers are terrible. And by that I mean that I hate them. Very disappointing compared to the rest of their line. At high volumes under stress you can hear the cone waffle and struggle. It sounds something like bat wings flapping around (not that I really listen to bat wings or anything, I'm just trying to describe what I liken the sound to). Oddly enough, the powered subs in their towers sounded incredibly better than their stand alone pieces and don't really suffer from any of the same problems.
In wall/ceiling stuff from them is OK. I wouldn't call it great and don't recommend it. Their new IP addressable speaker is extremely expensive and gets press because it is different/groundbreaking/new, not because it sounds superior to other products.
Sub/Sat systems from Polk disappoint me for some reason. They sound OK, but I feel that they fall short in the cosmetics department in a huge way. The sound from them is, as I described earlier very true, but almost muted in a sense. It's as if they are trying really hard but can't find a comfortable range. Plus a Polk sub comes with the set which is a negative (for me). I feel that product from a company like Canton is well worth the difference in cost (maybe $50 - $100) in this market segment. Infinity makes a neat little system with their TSS line as well. A much better subwoofer comes with their sub/sat systems.
Summing it all up, the short version of my take on Polk is: Very nice box speaker and worth auditioning in their price range to see if they fit your tasates. Outside of that, I'm not a fan. I like them better for movies than I do for music.
Alternatives: PSB makes a great product these days, listen to them. Infinity Beta's I like as well as their TSS sub/sat systems. I'm not a B&W (particularly in the price range of Polk) or Def Tech guy. Two brands I would highly recommend that you didn't list are RBH Sound & Canton.
Hope some of my opinion helps.
