Which Quantified Self device should I get?

After attending the Medicine 2.0 conference where I learned more about the Quantified Self (QS) community, I've decided that I want to get a QS device and I want to start tracking some of my own biometrics so that I can share that information with the QS community. When I exercise at the gym, I usually wear a Polar heart rate monitor, but that's about the extent of collecting quantifiable biometric data on myself.

There are a number of QS devices out there ranging from clips, arm bands, keychains, and watches. Which one should I get? Should I wait for some of these newer devices to get released? Or, maybe I'll end up using 2-3 of them simultaneously. That's my style of testing devices. That wouldn't be a true comparative study, but it would give me some qualitative data on these different digital tools.

Stay tuned. I'll share more information as I research QS devices and pick one (or two) out. Maybe this will be my Christmas present this year. I think I need more gadgets in my life.