TonyWilliams can correct me if I'm wrong, but if an aircraft is radar identified and proceeds to squawk 7700, the data tag will drop off and will be replaced with an emergency tag.

I'd much rather be talking to the controller, and him being able to see my callsign on the data tag. 7700 can wait for either if the controller tells me to, or if we got lost in a handoff, not talking to any controllers yet, etc.