There are two basic formats to Comparing or Contrasting two items. If one were to compare apples and oranges, for example, we would consider the fruits the items, and qualities such as flavor, color, texture, "juicability" and the like as the aspects.
Both are designed to evaluate the relative merits of two items so that the reader may come to some sort of conclusion. The writer's goal is to be as complete and fair as necessary; in other words, no important information should be omitted, especially any that would be likely to skew the overall picture from one side to another. Also, the writer must compare the same or similar aspects of the two items. One cannot fairly compare apples to oranges by merely comparing the oranges in juice form to the apples in sauce form. It would be fair, however, to include a discussion of the superior nutritive value of orange juice over that of apple juice. One could also discuss the "unsaucability" of oranges and compare it to the popularity of apple sauce. The purpose is to appear as unbiased as possible; if your favorite item is superior, then let it stand on its own merits.
The first style is side by side. The two items are compared aspect to aspect. Paragraphs focus on an individual aspect and explain how both items compare in that aspect.
Introduce Aspect 1
Summarize comparison Aspect 1
Introduce Aspect 2
Summarize comparison Aspect 2
Introduce Aspect 3
Summarize comparison Aspect 3
Overall Summary of Comparison
Explain which is superior
Explain what factors lead to that conclusion
Explain what detracting factors are overlooked or ignored
Summary-reiterate which item is better (one sentence)
Projection or Call to Action
Notice that organizationally the item that goes first in the first paragraph of the body then always goes first in every paragraph. Also , the writer needs to summarize each paragraph and determine the overall impact or result of that particular comparison.
Next is what I call A, then B. Examine all the aspects of Item A, then discuss those same aspects of Item B in the same order.