Someone once told me that you can judge a man's character on the happiness of his wife and the respect given to him from his children.

Mamma Corleone always respected Don Vito. She would never disagree with him in public (from the book) and seemed to always be very happy. She seemed happiest with her husband and family.

Kay, on the other hand, came off as being naggy and obviously disrespected Michael when she went through with an abortion knowing full well what it would mean to him.