The main difference between USB and ethernet is how they will be used. As you know, the USB is used in order to connect different things. For example, you would need to connect different peripherals to your computer like your mouse, your keyboard, your printer, and so much more.
The USB will make it easier for you to connect those things easily. What ethernet will do is it will make sure that information can be transferred easily from one device to another. For example, you would like to share details and information with multiple computers; this can definitely be achieved with the help of the ethernet.