These characters actually have a great deal of similarities in their role as substitute parents: both "adopt" a child in the form of Estella and Pip, and both do so for their own selfish purposes. Both do this because of the ways in which they have been hurt by others in the past. Both are characters who are therefore, if not necessarily evil, at least morally dubious in terms of their motives. However, at the same time, it is clear that they are very different in terms of their background and experience. Miss Havisham, for example, has always known great wealth and was born into a position of high class and fortune that she has enjoyed all of her life. Magwitch, by contrast, when the reader first confronts him, has sunk as low as he can possibly go, as an escaped convict. Note how Pip describes him in Chapter 1:
A fearful man, all in coarse grey, with a great iron on his leg. A man with no hat, and with broken shoes, and with an old rag tied round his head. A man who had been soaked in water, and smothered in mud, and lamed by stones, and cut by flints, and stung by nettles, and torn by briars; who limped, and shivered, and glared and growled; and whose teeth chattered in his head as he seized me by the chin.
What is so interesting about this description is that it captures the fear that Magwitch inspired in Pip, but it also shows the more adult Pip, looking back at what he saw as a child, through the later description of Magwitch as rather a pitiful man. The later sentences evoke pity and sympathy rather than fear and loathing. Thus one of the key differences between these two characters is their background, and the poverty and hardship that Magwitch has experienced, which is completely different to that of Miss Havisham.