Lee presents a careful contast between Atticus Finch and Bob Ewell. It is a good thing you mostly need differences, because Atticus Finch and Bob Ewell are not described as having much in common.
Both come from old Maycomb families. However, Atticus comes from a respected family and Ewell comes from an impoverished family that is universally condemned by the rest of the society.
Atticus said the Ewells had been the disgrace of Maycomb for three generations.
None of them had done an honest day’s work in his recollection. He said that some Christmas, when he was getting rid of the tree, he would take me with him and show me where and how they lived. They were people, but they lived like animals. (ch 3)
Both have a reputation that precedes them. Ewell has a reputation as a drunkard, whereas Atticus has a reputation as a straight-laced, moral man. Ewell beats his children and drinks away with little public assistance money they have. Atticus treats his children respectfully, and Miss Maudie comments that Atticus does not drink.
“If Atticus Finch drank until he was drunk he wouldn’t be as hard as some men are at their best. There are just some kind of men who—who’re so busy worrying about the next world they’ve never learned to live in this one, and you can look down the street and see the results.” (ch 5)
By contrast, the Ewells are described differently.
Every town the size of Maycomb had families like the Ewells. No economic fluctuations changed their status—people like the Ewells lived as guests of the county in prosperity as well as in the depths of a depression. No truant officers could keep their numerous offspring in school; no public health officer could free them from congenital defects, various worms, and the diseases indigenous to filthy surroundings. (ch 17)
While Ewell is an obvious racist, Atticus has a universal respect for the dignity of man. Bob Ewell seems to have no respect for human life. He is willing to try to kill children to get back at their father.