There are certainly many ways to have students compare things and to represent that comparison visually. Even more well-known than the comparison-contrast chart is the Venn Diagram . The Venn diagram is also very useful, as long as we keep in mind that the real value of a Venn is in the DOING of it...they work best when we have students, not teachers, determining what the relevant similarities and differences are between two or three concepts, people, places, or ideas. The website offers several types of comparison-contrast charts and Venn diagrams, which can be downloaded and printed out from the links below.
For a shorter paper, the above might represent three paragraphs; if you are writing a long paper and have a great deal of information, you may choose to write about each point, A, B, and C, in separate paragraphs for a total of six. However you decide to organize, make sure it is clear why you are examining this subject. You might be able to compare apples and oranges, for example, but why would you? Include any insights or opinions you have gathered. And yes, in general, three is the magic number. While there is no hard-and-fast rule that precludes creating a paper based on two points, or four, or five, a three-point discussion is manageable, especially for complex or abstract subjects. At the same time, a three-point structure helps you avoid oversimplifying, especially when addressing controversial topics in which discussions tend to become polarized–right or wrong, black or white, for or against. Three-point treatments encourage discussion of the middle ground.