My only experience with BT headset sound quality is with Motorola, H300 then H500. I compared receive quality to my Razr built-in earpiece as well as transmit quality by recording to my voicemail then playing back. The Razr has excellent audio quality. Both BT I would call adequate, not great. Not sure how much of the degradation is due to the Razr BT or the headset BT. Only extensive comparisons with multiple headsets paired with multiple phones will yield any conclusive results.
I have friends with Plantronics BT which they seem to like and I know to have better than adequate microphone quality with the phones they use.
Another thing I can tell you is, whereas I have confirmed the advertised maximum standby time of 200 hours in a strong digital coverage area, flip closed, never making a single call, just turning on BT in the Razr under the exact same test conditions drains the battery dead in 16 hours flat. Not happy with that at all.