I have the interactive and a bunch of the different color wrist ID bands and a couple of different colors of the ankle bands (Road ID was the presenting sponsor of Levi's GranFondo last year and everyone got gift certificates).

I chose the interactive because my medical info changes rather frequently, but there really isn't anything that I'm taking that should cause a severe allergic reaction so they don't need immediate access to my medical records. It's more so I can have more emergency contacts and update numbers as people change them.

The ankle ID is made of a more foamy material. The original wrist one is made of a nylon type material and isn't as soft. Depending on which one you like the look of more or which material is more comfortable, you can wear them wherever you want. Both Chris Horner and Levi Leipheimer are wearing ankle Road IDs on their wrists at the Tour de France (or have been that I've noticed, but I haven't noticed it every day). You may need a larger wrist one to fit on your ankle or a smaller ankle one for your wrist.