At this point, the best USB specification on the market is USB 3.1. USB 3.1 is not commonplace, so the average person has accessibility to USB 3.0. USB 3.0 is widespread, and USB extension cords have to have 3.0 accessibility to keep up. Most USB 3.0 extensions can transfer 5.0 gigabits per second.
USB 2.0 is on its way out. If you have had a webcam for a while, it probably uses USB 2.0. Luckily, USB extensions can still work on older USB cables.