This is a good question. If you are looking for the good and bad in people and you have chosen Boo and Mayella, then a few things come to mind.
First, both are bruised people. They have suffered in life on account of their family life. Boo's father was a religious fanatic, and Boo suffered his whole life because of this. Mayella's father was not a religious fanatic, but he was a drunk and absentee father who beat her. From this perspective, we can have compassion for both characters. In fact, Atticus makes this point in the trial. He has compassion for Mayella. Tom Robinson says the same thing.
Second, there is a big difference between Boo and Mayella. Boo, even though abused, acts in an honorable way. For example, he protected the children. Mayella acted in the opposite way. She accused Tom Robinson, an innocent man.
Here is a quote that indicts Mayella.
“I have nothing but pity in my heart for the chief witness for the state, but my pity does not extend so far as to her putting a man’s life at stake, which she has done in an effort to get rid of her own guilt.
In conclusion, even though we can understand why Mayella did what she did, she is not free from guilt. In her weakness, she sinned gravely by harming a "mockingbird." Boo, on the other hand, always chose what was right.