Jack leads like a tyrant. He uses physical force to impress and enforce his own rule. Over the course of the novel, he is able to scare and manipulate many of the boys because they are young and impressionable. Focusing more on hunting, Jack is able to produce food and this shows his ability to produce immediate results with his style of narrow-minded leadership. His leadership is simple and short-sighted. This gives him an appeal (in his clear demonstration of power) but this also shows his lack of vision in that he ignores long-term goals such as keeping the fire going to enhance their chances of being rescued.
Ralph is much more thoughtful and considers the boys' opportunities for rescue as important as securing their immediate needs of shelter and food. In the grand scheme of things, Ralph is the better leader. His leadership qualities are more mature, but because the boys are young and impressionable, he loses their loyalty as some of the boys are lured by Jack's more easily understood leadership. It would be wrong to say that Ralph's leadership qualities are "dangerous." As a leader, Ralph has all of the advantages over Jack because he thinks long-term and short-term. The problem is that the boys would rather play the hunting game with Jack than be responsible and work hard in Ralph's camp.
We see the dangers of Jack's leadership when he ignores the importance of keeping the fire going in Chapter 4. When Jack celebrates his victory of killing the pig, Ralph laments a lost attempt at being rescued:
“There was a ship. Out there. You said you’d keep the ﬁre going and you let it out!” He took a step toward Jack, who turned and faced him.
Ralph criticizes Jack and the other hunters for abandoning the shelters and the fire. Ralph establishes himself as the responsible leader but the others join in the chant of killing the pig. This represents a development from a civilized way of life (led by Ralph) to a more barbaric culture (led by Jack).