Atticus has three stark characteristics that contrast Bob Ewell:
1. Morality - Atticus cares to do the right thing. We see this as he makes the personal choice not to shoot animals that do not have the sense to get away from him. He realized the unfair advantage he had over other beings.
2. Intellect - Obviously if Bob Ewell doesn't care to send his children to school except for once a year, he really doesn't value education. Atticus so cares about it that he pays for his brother's term in medical school and forces Scout to go even when she fails to see the value in it. Atticus uses his intelligence to help others, even at the expense of not being paid completely.
3. Concern for Humanity - Atticus seeks the appropriate treatment of all people. We see this when Alexandra wants Cal fired, when Atticus defends Tom, and when Atticus struggles to hurt Mayella in an effort to defend Tom.