Honestly, one drive is going to saturate Firewire these days, so you really won't be getting full speed out of it with Firewire. It won't be horrible, but it won't be optimal.
I guess ill just stick with USB3 then. If I really need an extra port, I'll get a hub. Luckily my full size keyboard (apple) has two extra ports on it. Do you know whether those are USB 3 or 2? I'm thinking 2.