Go for a Firewire harddrive, don’t take a USB harddrive.
It’s true that USB 2.0 has slightly more throughput than Firewire 400. (Of course this doesn’t apply to Firewire 800, which is much faster, but then again I haven’t seen any Firewire 800 harddrives yet)
But the nominal throughput is nothing you should care about. What is important is the CPU usage. USB devices are much more CPU intense than firewire devices. With firewire, there’s almost no CPU usage visible while USB harddisks suck CPU like a freaking fourier algorithm on metamphetamines.
You don’t want to saturate your CPU just because you’re accessing your HD. DMA (direct memory access) already existed in the mid-70s (of course not in PCs, they began to appear 1980-82) and we’ve come a long, long way since then… and then some brainwashed interns puke out the USB line protocol during their lunch break to turn all that development down. Funny, I think.
