PCMacUser
macrumors 68000
USB 2.0 is currently faster than FW400 on paper, but there's a darned good reason that most of the audio interfaces produced in the last 7 years have been designed for FW instead - USB never lived up to it, and has a way higher incidence of dropped signals, clicking, popping, buffer underruns, and a host of other issues that royally screw up real-time audio recording and low-latency multitracking with virtual instruments and signal processing.
Audio interfaces require a lot of data throughput. Firewire 400 is faster than USB2.0 for these types of applications. USB's 480Mb/s is only its burst speed. Firewire's 400Mb/s is constant.