This is a tricky question since effective leadership involves garnering followers. If we look at the issue from a socially and morally appropriate point of view, certainly Ralph had better ideas about how to survive and be saved; however, I'm not convinced that made him the more effective leader. Jack certainly does a better job of getting people to follow him as evidenced by the number of tribesmen he has as compared to Ralph in the closing chapters.
I hate to make this comparison, but Hitler was certainly an effective leader. Obviously what he stood for and the actions he took weren't "right", but he was capable of raising a huge number of followers who listened to and believed in what he was doing. I believe that would make him a very effective leader - again, I don't believe what he was doing was correct, just an example of how leadership doesn't necessarily have to be "good" to be effective.
Logically, Ralph. He has the group's best interest at heart. He organizes shelter, food gathering, water gathering, and the rescue fire. He does not punish for no reason, and runs the "government" with fairness and justice...not fear. He is a President, not a Dictator.
Jack would make a better leader. Ralph failed to control the masses (littleuns). They run around when they should be building shelter.