I've used the Z9i and the V1 (similar to the Z1 I believe). I love them both. the only real difference is the voice command. if you want to be able to speak commands into the headset get the Z1, if not get the Z9i. either way you'll be happy.
I have the V1 and find it to be very comfortable. the headset comes with all kinds of pcs to customize fit just right. I wsa going to replace my original Jawbone with a Jawbone2, started playing with the Blueant V1 and have never looked back.
I purchased the z9i last night and started using it today. So far, so good. My original jawbone stop working so I was wired for a bit, then came across blueant. I spoke with their customer service yesterday and here is the differnce I was told. The z9i has call waiting feature and the V1 does not. I also looked at the v12 but that one does not have noise cancelling feature and lasts for about 10 hours of use.