At the beginning of the novel, Ralph displays better leadership skills than Jack. Ralph is the first boy on the island to take the initiative to organize the boys by blowing the conch. Ralph takes into consideration the importance of maintaining a signal fire and building shelters, which are both essential elements of rescue and survival. At the beginning of the novel, Ralph has the ability to gain the attention and trust of the boys. They look to Ralph for leadership and protection. Ralph develops rules on the island and effectively organizes the group.
By the end of the novel, Jack is viewed as the better leader, in terms of popularity and charisma. He is able to usurp power from Ralph and create his own tribe that promotes fun and savagery. Jack is able to motivate the boys to hunt and follow his directives, albeit through intimidation and violence. Jack successfully manipulates the boys' fear of the "beast" to advance his agenda. He recognizes the inherent primitive instinct in each child and is able to gain favor in the eyes of the castaways.
In my opinion, neither boy would be viewed a "good" leader for various reasons. Although, Ralph displays many positive leadership qualities, he lacks the ability to motivate the boys to work, and cannot quell Jack's uprising. Jack possesses the ability to motivate the boys to engage in his agenda but lacks the foresight to provide the boys their best chances for rescue and survival.