Callisto

"Craters are at home throughout the solar system, but nowhere more so than on the surface of Callisto: this moon has the oldest and most heavily cratered surface of any known planet or moon. Under the right terraforming circumstances, this could make for a particularly interesting (or a particularly difficult) landscape of lakes and ridges.Though less favorable than nearby Europa, Callisto is thought to contain a subsurface ocean that could harbor native life. It also has the lowest radiation levels of all the moons of Jupiter, so it makes a perfect place in which to begin our hominization of the Jupiter planetary system."