Choosing the right ethernet cable is going to depend on a few different factors depending on your circumstances and your personal needs. The most common ethernet options will come in a category 5 (cat 5) or cat6, but there are other options as well.
The cat 5 ethernet cables are made to work at 100 MHz, and they work for Internet speeds up to 100 Mbps. Cat 6 ethernet cables, on the other hand are wound tighter and will operate at 250 MHz. Many people look for fast network cables like 100 Mbps in hopes of increasing their speed, but the truth is that households with up to three computers can work perfectly well using a 10 Mbps ethernet cable.