The best model to represent the molecular arrangement of crystals is the space-fill model.
Crystalline structures are typically arranged in three dimensions, and space-fill models provide a more accurate visualization of the dimensions and volume occupied by the molecules in a crystalline lattice. They depict the relative sizes of atoms and how they pack together in a crystal structure.
While ball-and-stick models also convey structural information, they are primarily focused on bond connections rather than the true spatial arrangement that represents crystals. The options of Lewis dot and ribbon models are less relevant in the context of crystalline structures.