The best outline format in this case is the outline in topics.
Explanation:
Since your teacher wants you to describe your favorite character, the best sketch in this case is to outline topics. That way, in each topic you put characteristics of your character that will be relevant to your paragraph. For example, in the first topic you write the name and age of your character, in the second topic, write what novel that character is, in the third topic you put physical characteristics of the character in the fourth topic you write about the behavior of the character.
For example:
Hermione Granger
Fixed character in the Harry Potter saga.
Two physical characteristics of Hermione are her brown hair and her front teeth are larger than normal
