USB is sometimes faster, some times slower (1.5 (1.0), 12(1.1/2)*, 480(2.0/High-Speed) Mbps for USB vs 10, 100(fast), 1000(Gig-E) Mbps for Ethernet, commonly). The key difference is distance (3m for USB, 100m for above mentioned Ethernet) if you are only talking about two nodes.
either way,, your hard drive cant write as fast as they can send. So it really doesnt matter, unless you are runnin like a raid 5 across a bunch of drives
usb is rated at 400mb, and ethernet can go up to a gig, usually just 100mb though. If you are talking about a cable modem,,, it dont matter, cable modems only use like maybe 1% of the bandwidth the line can offer
USB 1.0 is way slower than 100Mbits Ethernet. USB 2.0 is faster. Anyway, I would go for Ethernet. Less driver trouble, better reliability. Easier to add switches, routers, hub's etc.
When i tried running my cable modem with a usb cord it tottally slowed down,Two of my friend's called me with the same problem and as soon as they switched to an ethernet cable it cleared up and was alot faster.
USB sucks. We had an ADSL USB modem and it kept sending data without any programs running, it was extremely slow, and once you started your computer you had to wait for 5 minutes before the internet worked. Also, when we shut the computer down and rebootet the "connected" light was lighting up, so you couldn't connect to the internet. We had to wait about 45 minutes before it had "cooled down" and we could start using it again.
The USB link cable we tried was even worse. We installed the drivers on both computers and it didn't connect or something. we uninstalled them but the computer kept remembering the allocated USB port blah blah...