Need advice on choosing Bluetooth OBD-II interface for application

[fuzzymoose]

I have an idea for a game that I want to program for smart phones. The game would record fuel economy data from a car to a smart phone using an OBD-II interface, and then upload that data automatically to the Internet. People can then compete with your friends on sites like Facebook to see who gets the best MPG every week.

Right now I am trying to figure out how best to connect a smart phone to an OBD-II port. I see that there are lots of Bluetooth devices on the market that claim to implement an ELM327 interface.

Does anyone have a recommendation for a good ELM327 bluetooth device? I'd like something that will work well with iPhone and Android.