It's a toughie isn't it....obviously Gordon Freeman would technically have some fascinating anecdotes but his muteness would mean he wouldn't be able to tell you any! Also the chicken breasts may remind him of headcrab flesh and make him cry.
Morgan would be a great laugh because you could spend the meal getting him to re-enact some of his famous narratives (March of the Penguins, Shawshank etc) you could even get him to narrate your consumption of your meal
And of course Martin seems like a nice guy, and you could probe him for any hilarious behind-the-scenes incidents that took place during the filming of the Office.
After much thought, I'm going for Morgan. But what about you? x