There are many characters, but the two characters that stand out to me are Jack and Simon.
Jack represents the base nature in humanity. At first social constraints keep him in check, and he even submits to Ralph's leadership. But as the story progresses and it becomes clearer that the boys will be on the island for a while, Jack's savagery emerges. He is obsessed with the hunt and in the end he even wants to hunt down Ralph. The point is that Jack represents the primordial passions of people. That most of the boys follow him apart from Simon, Ralph, and Piggy suggests that savagery is the default of humanity.
Simon, on the other hand, is very different. In my opinion, he is the opposite of Jack. He does not partake in the hunt or the things associated with the hunt. Not even Ralph can boast of this.
Instead, he is deeply spiritual and in touch with his surroundings and nature. From a moral point of view, he is pure, almost untouched by depravity. For example, he is kind to all the boys, even the younger ones. He is also insightful, as he knows that there is no such thing as the beast. He implies the beast is within. Moreover, as he is killed, he plays the "Christ" role in the novel.
By thinking of these boys as two archetypes, you can come to insightful points.