i'm with bytejuggler, i prefer external hd enclosure's because i have plenty of hd's already (you can always buy a new hd as well if you need to ) and i like being able to access them without needed to open up the pc. It's a lot more versatile.
one thing i will mention is that, firewire is superior to usb2. Even if the thoeretical bandwidth of usb2 is better, from experience firewire is more stable and fast for me.