A dictatorship (king, etc.) is probably the most efficient form of government. The caveat (and, of course it is a big one) is that the rule be benign and essentially selfless. On top of that, the ruler (and his minions) need to be intelligent and well educated. They must also not base their decisions on any religious point of view.
In practice this is difficult to establish and almost impossible for a second generation of rule. Heredity being unreliable and coups common. If real (as opposed to perceived) personal freedom is maintained, there would probably be general acceptance. If the rule is rational in its' actions it will conflict with the people whose view of the world is in someway divergent with reality. Therein lies the problems with democracy. It is ruled by money and power wielded by people with a broken concept of reality.