http://www.vxicorp.com/products/blu...le-solutions/bluetooth-headsets/b250-xt-plus/
This is the one I use. The joke is it'll make you look like you work at McDonald's (due to the massive battery, and thus talk times), but it's hands down one of the best ones to use if call quality is that important to you. I could hang my head out the window at highway speeds and the person on the other end could never tell. There's been times where I was on it next to a loud engine where I couldn't hear myself talking, but the person on the other end heard me perfectly with only a faint hum in the background. That's how good the nose cancellation is on those headsets. It also has a wide and loud volume range and the ear cup blocks out a lot of noise, so you'll never have to worry about hearing the person you're talking to. It's not stereo, but it can play media audio and works with Skype.
About the only downside other than size/aesthetics, is reconnecting after getting out of range. Usually it reconnects fine, but occasionally you have to press the action button to do it manually. Especially if it's for a long period of time. Rarer still, it won't reconnect at all and you have to reset it by plugging it into the charger while the charger is plugged into its outlet, then unplug and reboot. Never got a definitive answer if that's a headset issue, or Bluetooth, but it did it with my last phone too. Haven't noticed any additional problems on the M8.
If you don't like the over-the-head style Bluetooth, that company makes a couple other styles that wear differently. They claim to have the same nose cancellation properties and I've heard good things about them from users, but I haven't tried other styles myself.
Btw, I call into radio shows using this one while going down the interstate, as well as many other people. If it's suitable for radio, then you know call quality is good.