What quality does Pip have in Great Expectations that seems to appeal to his friends?I believe it is consistency in his actions or his intellectual honesty.
I believe that you are right, but there are also other traits that Pip possesses that make him a good friend, to most people. First of all, he is trustworthy and reliable; when he says he is going to do something, he does it. Think of all of the meetings he kept with Miss Havisham and Estella, even when they were of great inconvenience to him. He helped his friend, Herbert, in many instances, and always followed through on his word even with the criminal, Magwitch. He was trustworthy, reliable, and kept his word, even from the time that he was a small boy.
Another trait that Pip has is that he is amiable, and super friendly. He tends not to judge too harshly, and if he does, he keeps it to himself. He is always civil, kind and friendly to those that he meets. His kindness wins over the unique Wemmick, and as a result, Pip is let into his sanctuary of a home, when not many people are. He is kind to the unusual Wemmick and his aged parent. Pip is kind to everyone, even to Estella after she so harshly broke his heart; he is kind to Miss Havisham, even as he's criticizing her for her actions against him. So that is a trait that Pip has that people like. Closley connected with that is that Pip has a big heart. He feels things deeply, cares about people deeply, and has a deep sense of obligation and love. People can sense that, and respond positively to it.
I hope that those thoughts helped; good luck!