I quite enjoy the small, casual conversations that the Chief and Cortana exchange across the games. It really gives them both a 'human' side, and presents that they aren't simply faceless, alien killing machines, and that they like to joke around occasionally just like any other group of friends would. Anyway, onto specifics: "Sleep well?" "No thanks to your driving, yes." "So you did miss me.." However, my favorite line technically isn't really a line. It's an outtake. But its sheer hilarity and randomness always manages to crack a smile. "Next one who dies gets it in the rear from ME!" [Edited on 12.10.2012 6:38 PM PST]