I second the Firewire vote, it will work much better for the things you will potentially do with it too. It ends up being faster because Firewire is a constant stream of data instead of bursts of packets (like USB).
The connection is faster internally, but you will be running programs and your OS off the internal along with accessing the music on it. Lots of wear on your drive, and the potential for a hick-up. Again, definitely go with the Firewire external.