That all depends on what you want to do with the cam! I assume that you are refering to a digital camcorder.
USB is good for useing the cam as a webcam or transfering still pictures, but is no good for transfering high quality video to the PC. For this the only option is firewire as USB cannot transfer the footage at full quality. Firewire can also be refered to as ieee1395, iLink or DV. Many modern PC's will already have a firewire port installed or can be added as a PCI card for around £20 or less.