lol, firewire's faster but is newer technolodgy so some motherboard don't have it and not alot of things (relativly speaking) uses it. USB's slower but all computer has it and most devices uses it.
Firewire is the fastest. Do the research, you'll see even firewire 400 beats USB 2.0 by about 10-20%... If I have a choice, it's Firewire. But of course, some things just, or mostly come in USB(USB drives, keyboards, mice...)