Are you going to step right into a Death Knight first to see how the new Hero class works? Which of the classes has got you most interested in trying new things? I'm excited to see all the Shaman changes, and I've got a Shammy waiting at 70, so that's probably what I'll do first. As for the Death Knight, I kind of want to see that stuff on the live realms, though by the time the beta ends, the call of a new class may be too much for me to ignore.
What's up first for you when you log into the beta realms?