I think using the USB cable is better, but it depends how often you are uploading files to the PC. If you are uploading 10 times a day on average, like me, for an indoor macro setup and when you are removing the SD card for that, its contacts are quickly worn out and you can dispose your camera.
I have made a semi permanent USB connection with an extra USB cable between the (Pentax) cable that is connected to the camera and the PC. The camera is connected and disconnected in the middle between the two cables, which also saves the USB connectors on the camera and on the PC. So, my take is that the USB option is usually better because you are running less risk loosing the camera because of worn out connectors.
Wikipedia says that the lifetime of a USB connector is approximately 1,500 connect/disconnect cycles.
http://en.wikipedia.org/wiki/USB_connection