First off, I agree with you Grungecat about that it probably would be Grandpa Longneck who would win, except I don't think it would be a "close run" between him and Topsy.
Second, I agree with Malte on that the Great Valley does indeed have a democratic counsel, where the different species of dinosaurs are represented by their leaders. Topsy, being the leader of the Threehorn herds, would ofcause have a "seat" on the counsel. However, as you said Malte, they don't have one leader who decides everything, but tend instead to discuss the problem and possible sollutions before taking action.
This is where Littlefoot and the gang tend to show, that instead of having a counsel who debate all day, a leader who takes immidate action is sometimes better. In a way, the LBT movies show two different leaderships. The gang which sometimes, if not most of the time, is build on the "one leader" concept with Littlefoot taking most of the major decsions, while the Great Valley counsel shows the "all is directly represented" way, where all have to agree on the course of action.