The answer is B: the argument with the most reliable cited sources.
Historical research, like any other form of research, depends upon sources in order to make a verifiably argument. A reliable source, in a historical perspective, would be one that is founded on matter of facts, historical proofs and events that can be corroborated and verified through other research contributions or even further original research. For these reasons, a stronger historical argument would be one that is based on the most reliable cited sources.