Here is the difference between firewire and usb. At max ideal conditions, usb is faster than firewire (just slightly), but the two have different ideal conditions. Usb was created for short bursts of data (mice, keyboards, printers), while firewire was developed for streaming data (hard drives, burners). Either can do the other, just not as good. You see usb do everything, but firewire stays away from mice and stuff for costs reasons.
So if you are tranfering small packets of data (even like 100 1k files), usb is the way to go. But if you are doing anything normal (say bigger than a few k to huge, firewire should be you choice.