In my opinion all of them because they always ask for things in exchange for 10 turns of peace and so on. But if I were to choose I would choose Bismark and Ghandhi being the worst out of all them. A bit of the opposit from civ IV to civ rev from ghandhi. In civ IV he's much nicer. Also in Civ IV Montezuma seems more angrier than he is than in Civ Rev. I would say the least annoying in civ rev is Mao.