Here's my free advice, I'm sure I'm in the minority here:
1. I haven't had good experience with Bluetooth headsets and my blackberry starting with the 7290 then the 8700. Picking up call all the time or not disconnecting were problems. I'd say they worked 85% of the time, but that 15% was too frustrating so I went back to wired headset. The Motorola with the flip boom worked the best for me.
2. I agree with martin_j001. the ety*com is the best sounding headset I've used. The biggest negative is it doesn't have an ear clip so the mic tends to move down from your mouth. Go to HowardForums: Your Mobile Phone Community & Resource
and look for a AX2 Pro or search for Mr. Wiskers. I think it is on the Bluetooth section where they took the mic from the ety*com and added it to the Bluespoon AX2 Pro. They have detailed instructions or you can find someone to make it for you, I think they're selling for $200, maybe less now. I haven't read anything but good about these headsets.
3. The Nexzen sits in a drawer (somewhere) after a week of use. It works great in the car, or in my office. I was actually looking for it to see how it works with a softphone on my pc. Gennum gives you tuning software to change the mic settings and speaker but you have to use it at a PC, there isn't a way to change the profiles in the field. Gennum Nexzen has just come out with a new model.
Most headsets don't work well in the wind, unless it has a boom and windsock. I want a bluetooth headset that I can use outside. So the wind is one factor and outside noise is the other. In NYC there is always a wind blowing as the buildings create air passages and it is noisy, very noisy. DSP headsets I've tried can't cut it in Times Square, the clipping makes it unusable. Not just Time Square but most of midtown Manhattan. This may not be a factor you. For NYC the best I've found in the Sony HBH-300, no dsp and a boom mic.
The jawbone has the same problem with wind but I haven't tried it so can't comment on the clipping; from what I've read it is similar. You can search here and howard forums as there was lots of discussion about it, and no, it doesn't use jawbone voice conduction. In the car, some of my Bluetooth headsets sound great, incoming and outgoing. There are two or three jawbone conduction headsets reportedly coming soon for the past 18 months, the Motorola H5 (now H9?) and the Nextlink Invisio Q7 have received a lot of press but both are vaporware as far as I know.
4&5. The boom is reportedly the best, but it looks to big for me. Check Home
. He was fairly active in this forum and did a number of headset tests. I settled on the ety*com for the size and it works very well.
6. My suggestion is decide where you really need to use a headset. If it is in a car or office you'll probably be ok with a dsp like the Plantronics, Nexgen or Jawbone. If you're outside, you should look for a headset without dsp, noise cancellation and a windsock. I have, off the top of my head, tried at least six bluetooth and countless wired headsets. The ety*com has been the best compromise.
EDIT - one more comment, I have been using the Sony DS970 headset with a Samsung A707 phone. It sounds good on my end and works well outside but I've received complaints my voice doesn't sound good.