Some cameras are equipped with a diopter so you can adjust the viewfinder to your eyesight, which we've found very helpful. But if a camera only has an optical viewfinder, you can't see your images until you transfer them to a computer. Digital cameras are totally dependent on batteries and, especially if you use the LCD as your viewfinder, you'll run through more batteries than you ever thought possible. Using AC to power your camera is especially helpful when you're downloading images directly from the camera to a computer or from the camera to a printer. The adapter is also helpful when you're shooting indoors from a fixed position.
Manufacturers tend to favor one and use that type in all of their cameras.
While media is an important consideration when choosing a digital camera, it's not possible to present an in-depth look at each of the different types within the space limits of this article. But we will say that, at the present time, a number of camera manufacturers use either CompactFlash or SmartMedia cards. USB connections are easy and relatively fast. Serial ports have a tendency to be slow and finicky. Convenient, easy but not always the speediest method.