I've owned Polk for a bit over 2 years and have listened to or tried nearly everything from their current lines. As one pointed out, they are very good at their respective price points, but not for everyone. Other than the LSis, I think their weakness is in the tweeter. The RTis can get pretty harsh on some content without the right source, cables and power combo, but I liked them for both HT and music, detail, imaging and soundstage were very good, just not as refined as some other speakers I've heard. Midrange is excellent, bass is tight, but without a ton of power, you'll still will want a sub even with the 10s and 12s.
The current Monitor line is firmly in the middle between the Rtis and Rs. Don't quite image as well as the RTis, but have the sweet midrange, sound warmer, but not as detailed...still can play loud without breakup. If you like the warmer sound or don't have the coin for the Rtis, they are a nice solution. For strictly bang for the buck, the Rs are tough to beat since they are practically given away by Frys. They are not pretty, but offer the Polk sound and are surprisingly hard to upgrade out of. I listened to several well respected speakers from $500 a pair to $1500 recognizing that each was better, but couldn't justify the price for the increase in performance, including RTi8s for a month.
Arguably, the best Polk speakers are still some of their vintage lines back from the stereo years with no or few WAF or HT compromises. The early Monitor line, RTAs, LS and SDAs are really pretty special, fairly easy to come by at very reasonable prices and can compete with modern speakers at or well above their original price points. I listened for 20 minutes to a mint set of SDA 1Cs and that was it, I had to have them.
To each his own of course...