USB, regardless of what the speed spec says, is crap. A lot of USB hardware (interface chip, cables etc) and a lot of device drivers in operating systems are unreliable crap written by people who were thinking "mouse" while they wrote the driver that you hook up your important harddrive up to. USB also randomly falls back to slow speeds when it doesn't like something on the bus, and that fact is hard to discover from software. The designers omitted obvious feature, notably host to host (that's why you cannot connect two computer just using USB, but you can with firewire). Then there is that whole mess with USB interfaces that are either host capable or not, which plagues current cellphones. And to top it all off even if you are host capable on a cellphone then you need another special cable, probably costing more than the device.
All things considered I like Firewire better