What are some reasons why Calpurnia is a better mother figure than Miss Maudie in To Kill a Mockingbird?

Calpurnia is a better mother figure than Miss Maudie because she is stern as well as loving. 

Miss Maudie never really serves as a disciplinarian.  To be a mother figure, you have to be both affectionate and stern.  Calpurnia lays down the law while also being supportive of Scout.  She calls her baby.  Miss Maudie is more like a friend to Scout. 

Calpurnia is the only mother Scout has.  She teaches Scout right from wrong.  A good example of this is when Scout complains when Walter puts syrup on his dinner.  Calpurnia scolds her for being rude, and tells her that any visitor to her house is her company. 

Scout describes Calpurnia.

She was all angles and bones; she was nearsighted; she squinted; her hand was wide as a bed slat and twice as hard. She was always ordering me out of the kitchen, asking me why I couldn’t behave as well as Jem when she knew he was older, and calling me home when I wasn’t ready to come. (Ch. 1) 

Miss Maudie, on the other hand, is supportive of Scout.  She is there for her when Jem wants to play with Dill instead.  She stands up for her when the other women, like Miss Stephanie Crawford, pick on her. 

I hadn’t meant to be funny, but the ladies laughed. My cheeks grew hot as I realized my mistake, but Miss Maudie looked gravely down at me. She never laughed at me unless I meant to be funny. (Ch. 24) 

Miss Maudie is always supportive of Scout.  She always tells her the truth and never talks down to her. While Cal is her mother figure and Atticus says they could never live without her, Miss Maudie is her friend.  Scout needs both women in her life.  They balance out the influence of people like Stephanie Crawford and Aunt Alexandra.