How can I organize a compare and contrast essay?

There are two basic ways to organize your compare and contrast essay. Let's compare cats and dogs as an example. What are some categories that you can use to compare them? Veterinary costs, daily care, and typical personality traits are three possibilities although there are many more.

Now here is an organizational pattern                    In another organizational pattern you
where you cover cats first then dogs:                     cover cats and dogs under each category:

Introduction                                                                   Introduction
Cats                                                                              Veterinary costs
* veterinary costs                                                           * cats
* daily care                                                                    * dogs
* typical personality traits                                               Daily care
Dogs                                                                             * cats
* veterinary costs                                                           * dogs
* daily care                                                                    Typical personality traits
* typical personality traits                                               * cats
Conclusion                                                                     * dogs
                                                                                     Conclusion

I am often asked which organizational style is better. I've found that it really just depends on which one appeals to the writer. It never fails that a writer will end up liking one over the other.