Firewire Ethernet Converter Which External Hard Disk Drive - Firewire 800 Or Ethernet?

Which External Hard Disk Drive - Firewire 800 or ethernet? - firewire ethernet converter

I want more space on my new iMac for editing by videos. I work with Final Cut Studio and HD video editing. Is Firewire 800, or would have a hard ethernet better? What is the difference in transmission rates at all?