Klipsch Reference series or Polk Moniter/Tsi Series

Wrong section.

But to answer your question, speakers are hugely personal preference. I've listened to Klipsch's RF series and Polk's Monitor series (TSi are basically the same) and while I'm not of a huge fan of either, the Klipsch were a bit smoother sounding while the Polks sounded a bit muddy. Both are forward / a bit harsh for my liking, but the Klipsch are VERY efficient and more balanced IMO.

While I haven't listened to them, when it comes to budget speakers, I have heard many good things about Infinity's Primus series. They're a little more pricey but I'm also a big fan of Paradigm's Monitor Series 7 speakers (or Paradigm in general).

Whatever speakers you go with, I would audition them. Also keep in mind when purchasing speakers that the AVReceiver you have should be considered, because like speakers, receivers can sound warm, neutral or bright. Pioneer IMO is pretty neutral / a bit forward / bright sounding. Polk / Klipsch wouldn't be the greatest match IMO.

When I bought my Klipsch reference speakers a while back I looked at the Polk and Mirgae competitors. I really loved the sound stage of the Mirage, but the low end sucked and in a small room there would be no directionality. The Polk were nice speakers but the center channel always sounded like a wet towel was muffling the sound. Also I just love the clarity of Klipsch. Some people find Klipsch too bright or harsh, but I find then extremely clean. They are also extremely efficient so you don't need much power to get good sound out of them.