1. If you wanted to show the 3-dimensional shape of a protein, including all of the atoms composing it, you should use a ball-and-stick model.
2. If you wanted to show the general shape of a protein, along with some important functional details such as folds and coils, you should use a ribbon model.
3. If you wanted to show the 3-dimensional shape of a protein, including the backbone structure, folds, and coils, you should use a space-filling model.
4. If you wanted to show a generalized protein in which the focus is on the protein's function rather than its structure, you should use a schematic model.
5. If you wanted to show the 3-dimensional shape of a protein by showing the amino acid side chains and their interactions, you should use a wireframe model.