as far as i know USB 2.0 is faster then firewire but its speed varies, firewire is capable of a steady data stream rate, thats why a lot of digital video cameras come with a firewire port. in the long run firewire can end up being faster, even better firewire 800.
and if your computer supports it install a pci slotted e-sata and you can get blazing speeds from an external hard drive. the speeds are almost as fast as an internal hard drive (only a fraction slower because they run through a pci 1st) but in theory are capable of running an operating system without compromising system performance.
even better LAN over a gigabyte connection to a dedicated backup server (doesn't have to be a fast computer), thats what i have all my computers doing, they all automatically sync their data with a server in my house (in RAID) to keep everything backed up and safe. i use a pentium 4, 1gb ram for my file server.
