In my experience, USB isn't as stable as FW. Having to restart a data drive is an inconvenience, but restarting the boot drive is, well, a system crash.
The only time a FW drive has lost connection for me was when the firewire hub it was connected to decided to die... On the other hand, it might just be me and bad luck with USB enclosures, and good luck with FW enclosures (minus FW hubs 😛).