@cws910,
It must be both - balanced by the preferences and character of the people to be governed. And no, there isn't any ideal form; each has their own potential advantages and disadvantages. Just as cultures and peoples differ, so must their way of organizing their way of life. Further, any combination - due to being administered by humans - will have problems (please keep in mind; however, that when someone says "this is a problem", yet another will point to that same attribute and say, "this, we got right").
Far too much "it depends" on this subject to come to any single conclusion.