Both of these characters seem rather interesting choices to be heroes battling against the oppressive restrictions of a dystopian society. Montag for example, although he may look the part and his role may be suitable, being a member of the fire department whose job it is to police the censuring of books, morally seems to be rather ambiguous in terms of where his real loyalties lie. At times, the novel presents him as being rather indecisive, and he is battled over by both Beatty and Faber, representing respectively the banning of books and the freedom of books. Note for example what Faber says to Montag through his earpiece at the end of the chapter "The Sieve in the Sand":
"Don't listen," whispered Faber. "He's trying to confuse. He's slippery. Watch out!"
Bradbury therefore presents Montag as needing to be reassured and rather uncertain about his own thoughts and ideas in places. He, in some ways, represents a character that Faber and Beatty have to fight for, to persuade and to win him to their cause. Although eventually he does end up successfully opposing the government of this dystopian regime and all they stand for, the reader gets the idea that this is a close-cut theme. Montag is not your traditional hero therefore.
In the same way, Winston Smith can definitely does not fit the bill of being a hero who opposes his own dystopian society. Physically, he is presented as a middle-aged man with certain physical weaknesses who has a desire to rebel and to be part of the Brotherhood but whose every attempt to rebel is watched and noted by the Party. At times in the novel he comes across as almost a pathetic figure, as in the following quote, when he is doing his physical exercise, encouraged by the female through the telescreen:
"That's better, comrade, that's much better," she added encouragingly as Winston, with a violent lunge, succeeded in touching his toes with knees unbent, for the first time in several years.
Although there is a touch of irony in this quote, it clearly presents Smith as a man who is not physically in peak condition. Consider too the way in which he has no idea of how he can rebel and what he can do to oppose Big Brother. He throws himself into the power of O'Brien because he is a stronger character who can offer a concrete plan of attack. Smith is presented as a character who needs to be lead, whether it is by Big Brother, or by O'Brien. Smith and Montag therefore have quite a few similarities in the way that neither of them are depicted as "traditional" heroes.