Answer:
The answer is, of course, up to each reader and watcher's interpretation, and if you can give warrants and citations, any character could be an answer!
Step-by-step explanation:
It has been a few years since I've read The Crucible, but from what I can remember, there is definitely a point reached where no one could have stopped the hysteria, as anyone who opposed it would be labeled as mad or influenced. From a legal standpoint, however, Thomas Danforth held the power to call all court proceedings to an end and effectively end the trials and hangings. This may not have stopped the hysteria from continuing in the minds of the townsfolk, but could have so with time and would have definitely avoided the brunt of the violence to come.
Before said point, I would argue Abigail Williams had the most sway as she was the spinner of the original story, and if she came out with the full truth early enough, it would be hopefully easy for the entire town to have been derailed from the ideas of witchcraft.