The best type of model to represent the molecular arrangement of crystals is the space-fill model. This model provides a three-dimensional representation that shows how the atoms in the crystal are packed together in space, illustrating the overall arrangement and volume occupied by the atoms.
While the other models (ribbon, ball-and-stick, Lewis dot) can be useful for depicting specific aspects of molecular structure, they do not effectively convey the three-dimensional arrangement and packing essential to understanding crystalline structures. The crystalline arrangement is inherently three-dimensional, making space-fill models particularly suitable for this purpose.