Better is a relative term. It's what will sound best to YOU. I have the Yamaha RX-V371 receiver and have been very happy with it. I think the only difference between the 371 and the 373 is the auto-cal on the 373 and a front iPod connector (?). Onkyo makes good systems but there have been some reports of issues (but any mfr can have issues from time to time). I think the Polk speakers matched with the Yamaha RX-V373 would probably give you a better all around sound stage than the speakers that come with the Onkyo or Yamaha HTiB (or any HTiB for that matter).
what about JAMO s608 are it is better then Polk ?
If you're comparing the Jamo S608 towers to little Polk RM705 satellites I would much rather have the Jamo. Not even a tough decision.