Use Your Gamer Launch Account
Your account from any Gamer Launch site is valid here.
If you already have a Gamer Launch account connect your Facebook account on your user profile first before using Facebook connect to login. Otherwise you may end up with a new account.
Quick warning, my spam filter picked up an email supposedly from ANET titled "Guild Account Be Shut Down Inform". Anybody who sends me an email with that kind of title would have roused my suspicions regardless of my spam filter. That said, obviously my account is fine and only a fool would click the suggested links. Be warned Guildies.