Practically speaking they are pretty comparable, so there are probably 4 issues that would decide:
- Availability - what can you get where you live.
- Cost. Apparently the reason you see so much USB 2.0 stuff is that it's cheaper to build; Firewire chipsets cost more.
- Connections. Depending on your particular setup you might have / find it easier to add USB 2.0 vs. Firewire to your existing rig.
- Other uses. If you do digital video editing or want to run a Firewire network, it may tip you to Firewire.
The speed comparisons are generally about the same, USB 2.0 is theoretically faster but more of that is overhead.
Though USB 2.0 is rated at a higher throughput speed, FireWire delivered faster performance on external hard drives when connected to a desktop. ... [but] since nearly all new mainstream desktop PCs have USB 2.0 ports, USB hard drives will be the market winners.
For CD-RWs, test results were a mixed bag, though USB 2.0 showed a slight edge. - PC Magazine article
Don't be confused by the rated speeds you see emblazoned across USB 2.0 and FireWire product boxes. Despite USB 2.0's 80 Mbps speed advantage over FireWire, our [hard drive] testing showed that the additional overhead of USB 2.0 made it slower than FireWire. ... On a positive note, we noticed that the CPU usage of each interface was similar on our Pentium 4 1.3-GHz test system. During a 1.54GB data transfer from our system's internal hard drive to an external drive, USB 2.0 averaged 40 percent CPU usage compared to 37 percent for FireWire.
[Firewire] also happens to be a great networking interface. Windows XP and Apple's OS X natively support networking with FireWire, providing an easy way to create a faster-than-Ethernet LAN.- link