I have heard that the Fitbit is not as good as the BodyMedia Armband. I have the armband and I absolutely love it. I'm not real happy about having to pay extra after the first three months for a subscription, but i will probably pay it because I don't want to buy anything else.
I really like that it gives you your sleep patterns, your duration of sleep, and this is very helpful to me. Sometimes I have slept for what I thought was 8 or 9 hours and it comes back and says that I really only slept for 6.75 hours. It also counts your footsteps, you can get a heartrate reading if you download the free software for it, and we are now able to sync to Spark! It gives other info as well. I wouldn't trade it for anything else.
Hope that helps!