I have been using the Plantronic's S11 for about 5 years now. It is wired but worked really well. The sound was perfect and I never had a complaint. Wanting to go wireless, I read reviews and felt the CS55 would fit my needs. I ordered it on Amazon and installed immediately upon receipt. My initial impressions were "so-so". It was a nice upgrade to be wireless but the headset did not sit firmly against my ear (using the over-the-head attachment), the sound was a bit "airy" - hollow-sounding. It definitely was not as good as my S11. I also heard my own breath often during calls. Whether it was from a sigh or just during the normal air release from talking...it was very annoying. I fiddled around with the controls for a long time and made about 35 calls to my wife to test (she was annoyed). I never got it correct and called Plantronics. They walked me through all the controls but still could not eliminate the 'wind' sound. I never once had the wind sound from my S11. So I returned the CS55.I then ordered the CS361N. I talk frequently to someone else with this headset and his voice is always clear. He raved about it. After plugging it in, I made my first call - to my wife again. No adjustments...and it was perfect! I could hear VERY clearly and the ear phones sit securely on my ears. I could bend over and move around and it did not feel like it was going to fall. My CS55 fell off several times during light movement behind my desk.I also know someone that recently bought the Jabra GN9125 and he sounds "airy" - or hollow.I wasn't sure I would like the stereo sound of having two ear pieces but it really is nice. My office is quiet so distractions are not an issue but it really forces me to focus. I'm sure I would also be happy with the Monoural CS361N.Hope this helps!