FireWire Vs. USB
USB is certainly the more popular of the two: almost everything has or can use a USB port, so a PC pretty much needs to have them. Furthermore, FireWire is more expensive in terms of licensing and hardware than a USB port. Therefore, when in doubt, a manufacturer will add a USB port before they add a FireWire port. USB’s ability to go from version 1 to 2 without changing the plug or socket, while FireWire 400 connectors underwent even a minor change probably, didn’t help.
But, as explained here, USB isn’t always the best way to go. Allowing almost anything to work with anything requires USB to rely heavily on software drivers, which end up having to share processing resources with the rest of your computer.
While FireWire may have fewer applications than USB, what it does – it does better than USB can. One advantage is the aforementioned peer-to-peer connection potential. This is one reason that FireWire is preferred to USB for connections related to digital video and audio.
FireWire is also a better choice for external drives. For one thing, it often takes 2 USB ports to deliver power to a drive, unless you are using a separate power adapter. The shared power of the USB bus can cause problems as well if there are too many USB devices plugged in. FireWire can deliver enough power from a single slot, not just for a 2.5" external drive, but, at least theoretically, a 3.5" one (good luck finding one though).