Which is the best government? That which teaches us to govern ourselves.

[Welche Regierung die beste sei? Diejenige, die uns lehrt, uns selbst zu regieren.]

Johann Wolfgang von Goethe (1749-1832) German poet, statesman, scientist

Sprüche in Prosa: Maximen und Reflexionen [Proverbs in Prose: Maxims and Reflections] (1833) [tr. Saunders (1893), “Life and Characters,” #225]
    (Source)

From Art and Antiquity, Vol. 5, #3, Individual Points (1826).

(Source (German)). Alternate translations:

I am asked: which is the best government? That which teaches us to govern ourselves.
[tr. Rönnfeldt (1900)]

You ask which form of government is the best? Whichever teaches us to govern ourselves.
[tr. Stopp (1995), #353]