I have used a number of Bluetooth headsets over the years and have had varying levels of success.  My needs are pretty basic, the most important features for me are:

1. Sound quality
2. Battery life
3. Wearability

I spend a lot of time on conference calls while driving so sound quality and noise cancelation are the most important feature.  I often more than 4 hours a day on the phone so batter life is a close second to sound quality.  I wear glasses so wearability is important because several headsets don't fit well if you are wearing glasses.