Long ago in the time of dinosaurs, slates and my college days, I remember reading something about forms of government and what was best. In an ideal world, the worst form of government is a democracy, with a Monarchy being the best. Since god kicked us out of that world 6,000 to 6million years ago, the best form of government in the non-perfect world is the democracy (or representative democracy) and the worst a monarchy.
Monarchy is not technically a form of government but a form of state. Monarchies are different from republics in that the sovereign is not the people (as it is in a republic) but a prince (possibly even a foreign prince) of some kind.
The United States and the (past) Soviet Union are republics, but the Soviet Union wasn't democratic.
The United Kingdom and Saudi-Arabia are both monarchies, but the United Kingdom is not a dictatorship.
Both monarchies and republics can be democracies (or representative democracies). And both can be dictatorships or anything in between.
My own definition of "dictatorship" puts in contrast to legitimate government, which in my opinion doesn't have to be democratic. I define a "dictatorship" as any system in which the ruler's power is limited neither by a constitution nor by tradition. (Both a constitution and traditions may allow for elections as a method to control the ruler.)
North-Korea is a republic. As is Libya and Saddam's Iraq. Jordan and Luxemburg are not. Nevertheless I consider the last two states with legitimate governments. (I don't consider the Saudi "king" legitimate. He says the constitution is the Quran, but in reality Saudi power is limited by absolutely nothing.)
Personally, I like monarchy and democracy and accept a republic only as a worse alternative. I find that having the people be the sovereign only creates an imbalance when one group has power over another. (This is not a problem when the nation is formed by agreement as in the US or Switzerland.)
But the three most important features of any state are stability, justice, and democracy; in that order.