The serial interface is much slower than the USB interface. Memory card adapters or memory card readers can transfer images much faster than serial cabling. Card adaptors or card readers may be installed on most computers. The computer will recognize the card as if it were an additional harddrive installed on the computer. This will allow the fastest transfer time from the camera to the computer.
Several companies have card readers available.
JPG or JPEG format is a good storage format. This format is normally compressed and reduces transfer time if you are sending files via internet or email. I you open a JPG file in an editor such as PhotoShop and resave the image you are recompressing the image. And every time you save that image as a JPEG, it's recompressed, losing more and more information with each generation. It's like crumpling up a sheet of paper, smoothing it out, crumpling it again, and again - only worse.