At the heart of this question is a very disconcerting thought: how much does one value one's own life? Is it worth one other, ten others....No right answer here. Even a billion lives would mean less than the one I know and live, wouldn't it?
I wonder the same thing as Jeno, what's the difference really between 100 and 1 billion people if they've done no harm and their fate lies in my hands. Why should there be a threshold and what determines where this threshold lies.
The truth is, I value myself greatly and would almost always pick me. Not because the other people deserve to die but simply because I value my own life greatly. I am also aware of my own potential and what I have to offer the world.I don't have this information for others so really can't make an informed decision favoring them.
Having said the above, sacrifice would make sense for people I love. I'd gladly give up my life for the few people I value MORE than my own life. If the odds of people I love getting selected in this random sample goes up to 1/6 - with a billion, then I'm out. They live, I'll take myself out.