So many real beauties, but bar none, the one I listen for every time is
"Nobody's business but ours." The way his voice cracks there is so heartbreaking.
And I know we're not talking non-verbal moments right now, but one of Heath's that's really struck me on the last couple of viewings is when he reads the first post card from Jack, the way he reads it silently the first time, stroking the sides of it with his thumbs as if it's a piece of his soul, and then the way he reads it a second time, mouthing the words.
Back to the topic at hand, if I had to pick one, I guess I especially like the way Heath delivers the line, "You got whiskey, or sumpin'?" Don't know why, but it just rings particularly true to me.