Oliver Twist is populated with some clear heroes and villains, and some in between. The protagonist is young Oliver, an orphan who runs away from an abusive country parish to live in London.
Oliver is clearly one of the heroes, because even with all of the bad influences he never turns bad.
'I am running away. They beat and ill-use me, Dick; and I am going to seek my fortune, some long way off. I don't know where. (ch 7, p. 34)
Oliver is generally a virtuous boy, but since the story is a progress he does not directly influence events—they influence him. He manages to stay good, despite falling in with a very bad crowd. He never becomes a criminal himself.
Dickens would likely have classified Nancy as a virtuous character. He believed that prostitutes were victims of society, and not bad themselves. Nancy is kind to Oliver.
Brownlow and Rose Maylie are the heroes of the story. Brownlow manages to pull Oliver above the fray. He sees his potential, and rescues him from a life of crime.
Some characters Oliver meets are neither heroes nor villains. When he makes it to London he is taken under the care of The Artful Dodger, a boy who is much less than virtuous, it turns out.
Jack Dawkins may be an apprentice of the fence Fagin, and on the wrong side of the law at that, but he is not all bad. He does seem to care about Oliver.
The Dodger said nothing, but he smoothed Oliver's hair over his eyes, and said he'd know better, by and by... (ch 9, p. 42)
Dodger does leave Oliver to get arrested, but he does not want to tell Sikes where Nancy is.
Charley Bates, interestingly enough, seems to be a good friend to Dodger. When Dodger is accosted by Fagin for losing Oliver, Charley seems to distract him from throwing a pewter pot at his friend.
Charley Bates, at this moment, calling his attention by a perfectly terrific howl, he suddenly altered its destination, and flung it full at that young gentleman. (ch 13, p. 58)
Charley is generally not a virtuous character, but like Dodger he cannot be considered all bad either.
There are two characters who are all bad.
Fagin is a greedy and violent character. He is physically abusive to the children he collects, and he turns them into criminals. Although he gives them a home, he also makes them steal for food.
Sikes also is a clear villain. Fagin’s associate and Nancy’s mate, he is coarse and cruel.