I go for Monarchy then Democracy.
If you have built all improvements and have many Wonders and you have Great Unit Power you can prevent War weariness by not losing many units when at War.
Democracy is indeed better if you have established Great Power and maintain your dominance. The main thing is to not lose Units and finish Wars quickly, which you can do IF you have the Power = improvements, Wonders and Units with many cities displaying "We Love The King".
If you have built all improvements and have many Wonders and you have Great Unit Power you can prevent War weariness by not losing many units when at War.
Democracy is indeed better if you have established Great Power and maintain your dominance. The main thing is to not lose Units and finish Wars quickly, which you can do IF you have the Power = improvements, Wonders and Units with many cities displaying "We Love The King".