No, I agree that Khan was the most dangerous. He was brilliant, ruthless, obsessed, and wanted to kill everyone, and then conquer the universe. Also, it took Spock sacrificing his own life to finally foil Khan for good. As for why he is considered to me Kirk's Joker, it's for several reasons. One, Montalban was fantastic. Two, Khan and Kirk had a personal rivalry. Three, they made the Moby Dick analogy very relevant to Khan. Also, Khan killed Spock, so of course he's going to say that.