I edited your original question, so I hope I was able to keep its intent intact. If not, I do apologize. I did feel a certain vagueness to the question, so I think you might have to sift through many answers in formulating “the answer.” There are many characters and decisions that have to be faced in Bradbury’s book. The most obvious of these is Montag and whether or not he is going to question the reality with which he is presented. This happens in the formative stages of the book, in that he has a decision to make in terms of accepting the reality that surrounds him or whether he is going to engage in a process of questioning that will reveal unknown, and perhaps, unwanted, results. This is a decision that puts into motion the events of the rest of the novel. Beatty has a choice when he realizes that Montag is changing and to challenge this becomes how he resolves this decision. Even Clarisse has a conscious decision to make. The mere fact that she is different from the rest of the social order and values different realities consists of a choice that needs to be made. Through her character and perhaps all of them , Bradbury might be arguing that individuals in the modern setting have a critical decision to make as to whether they are going to be a part of a social and collective whole even when they recognize that it is progressing down the right path or are they going to activate their voice of dissent in articulating a vision of what should be as opposed to what is.
Montag, the main character, makes some of the most important decisions in this book. First of all, he choses to reject the society he had spent all his life in and instead pursue the forbidden knowledge of books. His wife Mildred, on the other hand, is unable to let go of her society and especially the walls of her parlor, which she is clearly addicted to. Beatty also choses to adhere to society, but for different reasons. He used to be a lover of books, but came to reject them when he was unable to find comfort in them. Beatty opposes Montag's efforts to destablize their society, and is killed by Montag. Montag's professor friend, after years of hiding, is inspired by Montag to be brave and oppose the horrible society that had kept him in immobile in fear for so long.