The Ewells, Cunninghams and Finches represent three different levels of the Maycomb social structure in To Kill a Mockingbird. The Ewells are the lowest of Maycomb's white families, "the disgrace of Maycomb for three generations." Father Bob does not work, beats his daughter, and allows his children to go to school hungry and lice-ridden. Mr. Cunningham is even poorer than Ewell (he will not accept government financial assistance), but he works hard to keep his farm productive. His children are often hungry, but they are clean and respectful. Atticus' family is one of Maycomb's elite, and he is probably the most respected man in the town. His children are never wanting in the essentials of life, and they thrive at school.
I guess I would say that the difference here is that a Cunningham and a Finch are good while a Ewell is pretty much of a disagreeable person. The Ewells are really the major villains of the book.
The Cunninghams and the Finches are not completely alike. The major difference is that the Finches are higher up in society and much better off economically. But both have solid values and try to do their best in all ways.
By contrast, the Ewells are kind of trashy. They do not seem to take showers very often. They are not hard workers like the other two families. They end up being violent as well.
In the book To Kill a Mockingbird one gets some insight into the different social status of some of the families within the story.
The Ewels represent uneducated poor disgusting and trashy southerners. Mr. Ewel is an alcoholic who rapes his own daughter and beats his children. He has no respect for the law until he needs to use it to his own advantage. Even in the courtroom he does not demonstrate respect for the attorneys and judge. He also does not value education or work. He is a dishonest and disrespectful man.
The Cunninghams are also a poor family but the man has dignity which he deomstrates by repaying his debt to Atticus through barter. The children attend school even if they have no money for shoes or decent things and even food. They have been taught to be respectful to adults. Mr. Cunningham will not take hand-outs and has a great deal of pride.
The Finch's are a line of southerners who have the respect of the community. They are relatively hardworking honest people who have comfortable lifestyles and respect the rights of other people. They represent middle class America at the time of the book. Although there is a depression, they have food and a housekeeper.