But USB is....TERRIBLE. Just listen.
SOME USB is terrible. Not all. It really depends on how it is implemented.
Another Firewire option if you don't want to drop large coin on Audiophile gear is the Focus Saffire or Saffire LE ($299), which is a pro piece and requires some savvy to use the interface. Apogee's choices would be easier to use though (being more of a plug-and-play experience).