This is a little off the wall, but why don't you register them both, and then as your first users what they think? Have a vote. Get's them involved in the site,

This is a little off the wall, but why don't you register them both, and then as your first users what they think? Have a vote. Get's them involved in the site, and makes them feel special, like all early adopters want. A little off the wall, but it solves your problem with little effort.