Anyway, with the advent of the new USB 2.0 spec, both protocols have about the same speed, if we exclude Firewire 800. USB 1.0 is mostly used for keyboard and similar devices that don’t need fast connections.
For me, the biggest selling factor for Firewire is the star-based protocol, versus the client-server protocol for USB. This means that you could hook together multiple Firewire devices. With USB, you need to have hubs between in order to have multiple connections working.
The other thing good to remember is that in both cases the protocols provide charging via cable — you just need six-pin Firewire connectors (some PCs only have four-pin connectors). However, the amount of power trickled via the ports could drain the battery fast, or even worse, cause problems with external firewire devices due to sudden blackouts of power.
So, if you use Ableton Live or something similar with external Firewire or USB 2.0 audio boxes, always provide external power to avoid problems during live shows. You could also get hubs that provide external power, but it’s just best to plug the external devices with their own power supply.