I think a perfectly designed AI would be a better ruler than any human, at least thats what I took away from the Scythe series of books by Neal Shusterman. Every human can eventually get corrupted, and even in democracy a bad apple spoils the bunch as it takes just one corrupt leader to topple the tower. But AI can manage everything with 100% efficiency & morality because its brain can be expanded infinitely. Theoretically an AI could feel empathy and be kinder than any human ever could, as well as be uncorruptible. The only problem is every human has biases so a man-made AI would have the flaws of Man. Really interesting question though!