Audio Interface or HDD Firewire?

Which would benefit me more: having my external HD hooked up via firewire or my audio interface? I'm working with Logic Express 8 and the Macbook in my specs.

It depends.
Hook up your HD if you are just using samples or projects off of it for Logic .
Hook up your audio interface if you are directly recording from other hardware into Logic.
Or do like I do and have them both hooked up via FW. ;D