According to a recent lecture at Stanford University, federalism as a form of democracy is the "best" form. From the lecturer:
In a democracy, the exercise of political power must respect the law, the constitution, and the will of the people, through the decisions of their [elected] legislative representatives. This requires that power be separated so that the head of government and his ministers do not have the power to make the law or to interfere in court cases. In a democracy, the executive branch implements policies and programs, administers the national budget, and conducts national affairs. It may also propose laws, but only the parliament may enact legislation, including the budget. Only the courts can decide the guilt or innocence of individuals charged with a crime, and only the higher courts can determine whether a law or a government action or policy is constitutional.
Why is the concept of the separation of powers so integral and vital to a strong and lasting democracy?