[Daox]

The normal Prius liftback is virtually the same as the V, except they extended it about 6 inches, the back isn't sloped as much, and its been regeared a bit to maintain good acceleration (at the expense of gas mileage). The Prius C is smaller, and it also uses a smaller engine. The best way to really know what you're looking at is go look at them. The size difference is noticeable.

The liftback and the Prius C have virtually the same mpg ratings. The C gets better mileage in the city, and the liftback gets better mileage on the highway. The V gets the lowest of them all. If you look at fuelly.com (actual user data), the Prius Cs are averaging 51 mpg, liftback is at about 47, and the V is at 42.