Ethernet comes in three flavors: 10 megabit, 100 megabit, and gigabit. That’s geek speak for 10 million bits per second, 100 million bits per second, and one billion bits per second. In all three cases the actual speed is more like 60 to 70 percent of the maximum speed.
The most common form of Ethernet, 10 megabit, offers actual throughput of six to seven megabits. USB 1.1 tops out at 12 megabits. It’s nominally faster than generic Ethernet. For sharing Internet access either is fine, since even the fastest broadband connection never exceeds one or two megabits per second.
On the other hand, if you’re shipping large files from computer to computer inside your network you might want a faster connection such as 100 megabit or gigabit Ethernet.
Companies have introduced USB 2.0 network adapters that are theoretically much faster. USB 2.0 is nominally capable of 480 megabits per second. However, this isn’t the actual speed in real world conditions.