I had a difficult time finding a bluetooth headset that I really liked. I have spent a lot of time, and money, trying several styles. This is how I would rank the ones I own:#1. Sound ID SM100 Ear Module Bluetooth Headset. Best ear fit, sound is sharp, clear & crisp. When not on the phone the headset changes to a listening mode and hearing through it is very easy. Overall my favorite.#2. Plantronics Discovery(tm) 665 Bluetooth Headset. This one also has very good sound but a bit muffled, not quite as crisp as the Sound ID but still very good. If you prefer a softer sound, not as sharp, this one would be best. It is also the lightest weight and fit was quite good.#3. Aliph Jawbone Bluetooth Headset. I just couldn't take to this headset. I found it a bit awkward, the fit in my ear was just OK. The sound was tinny, kind of like listening through a tin can. I could hear but it was harsh sounding. This one did have the loudest volume.I found myself mostly using the Sound ID, occasionally the Plantronics, and never the Aliph Jawbone.VERY IMPORTANT: If you wear your headset a lot, and are looking for the ultimate in comfort, try a custom made earpiece from: www.averysound.com. They have a kit that makes an impression of your ear and can make it fit just about all headsets. The ear piece that you get is feels like soft latex, actually feels like one of those gummy candies. The fit is perfect and the earpiece stays rock solid in your ear. It also blocks out all outside sounds. This is both good and bad I guess. If you use the Sound ID this is less of a problem as it allows sound to pass through it when you are not on the phone. A nice feature. The only downside I found is that these earpieces are a little bulky. Otherwise these are really amazing and the ultimate in comfort.I originally had one made for the Plantronics, and one for the Jawbone. I bought the Sound ID later. Since I do not use the Jawbone I put that one on the Sound ID and it fit perfectly.Another headset I can recommend, for those who don't mind a full size telephone operator style is the: VXI BlueParrott B100 Wireless Headset System. These are really superb. Excellent sound and very comfortable. Only problem is the obvious; they are large. Great for use in an office setting. I can highly recommend these.