Throughout the Cuban missiles crisis there were scores of decisions made, all of which in the end prevented the 3rd world war. The movie "Thirteen Days" beautifully portraits how this crisis was handled by our government. The first important decision was JFK giving the go ahead to Bobby Kennedy to create a "think tank", ExComm whose job would be to think of the best possible course of action. I consider the decision very valuable because it was ExComm that came up with the idea to create a blockade or quarantine around Cuba. With the decision to go with the blockade, the world was saved from probable nuclear destruction. JFK didn't have to allow for ExComm to be created, or allow for new ideas to be heard. He could have simply gone with the proposal the joint-chiefs of staff gave, of air strikes/invasion. The same proposal which would most inevitably lead to world war, or yet worse, a nuclear destruction.
Another important decision was made by JFK right after Major Anderson was shot down, when he didn't listening to the chiefs and ordered them not to retaliate on the samsite, which would be the spark that would lead to a fire of destruction. JFK could have gone along with the "rules of engagement" which would call for immediate attack on the sams, therefore hindering any chance of political action.
The finial decision which proves it self to be momentous was the decision to ignore Kruchev's 2nd letter and accept his 1st. With this we would trade the missiles in Turkey 6 months later, dismaying any thoughts that the U.S. was trading under threat, and resolve the escaladed situation. The only other choice open at the time, was that of war.