Neither character can actually be accepted as a revolutionary. Revolutionists change the situation, often for the better. Although the idea is discussed throughout the story and readers hope for revolution to occur in this dystopia, revolution is never realized. In fact, both Julia and Winston are broken in the Ministry of Love and come to the point themselves that they love Big Brother. In the very last chapter, readers watch a possible interchange or reunion between Julia and Winston, but the thought and emotion was beaten out of them. They no longer have the capacity to feel for themselves, let alone each other.
Because readers get to see Winston's thoughts, they know that Winston longs for revolution, but lacks the intellectual capacity to orchestrate anything on his own. This is why he had hope that O'Brien might be a leader that could help.
Julia could lead a revolution. She did have routes mastered in which she and Winston did not get caught by the Thought Police. She has the desire to rebel and the sense for sneakiness, but she lacks the care to pull off a revolution.