Like Brian said, ethernet is more common and usually cheaper.
If you ever intend to change operating system, ethernet seems a better choice and if you want to network several computers, you will probably be better off with a ethernet card.
You can also get longer RJ45 (ethernet cables) if you move your computer further from the modem.
My experience has been that USB just isn't as stable a connection as ethernet. Just my humble opion.
A forum community dedicated to tech experts and enthusiasts. Come join the discussion about articles, computer security, Mac, Microsoft, Linux, hardware, networking, gaming, reviews, accessories, and more!