I voted for the first choice.
We are dealing with a hypothetical scenario within a story. So, its far easier to tackle this then in real life. A lot of it depends upon specific circumstances. But the idea that you won't let one person die so that twenty can be saved is wrong. At one level it sounds heroic. It speaks of principles and morality of a lofty nature, which i definitely desire to see in more characters. And it is one of the reasons, i prefer Superman over any other superhero.
On the other hand, if we are speaking about morality which is practical and useful, this is useless. To sacrifice a person to save a family is better. To sacrifice a family to save the city is better. It is better to sacrifice a city to save a nation. Its better to sacrifice a nation to save the world. Its better to sacrifice the world to save the soul.
For the sake of this topic one may ignore the last part. Its from the Mahabharata and that part speaks about the importance of spirituality and renunciation. But that is not just a religious text. Its also about practical morality. To be 'religiously' moral in this world is not possible, as there are immoral people, with whom moral people have to contend with. And even the most moral person has to sometimes give up morality for the sake of a higher cause. Situations arise in life when an immoral choice is actually the moral one, and the moral choice is the immoral one.
That book demonstrates this very effectively. The story of Mahabharata goes something like this. The eldest child who should have been the king is blind from birth. So, the younger son who is equally qualified becomes the king. But he dies at a young age leaving behind five sons. The blind elder brother, becomes for the time being the king. He has 100 sons, called Kurus who are evil minded, lead by the eldest Duryodhana. The five sons of the younger brother are men of highest moral caliber and qualified princes called Pandavas. This leads to conflict as the Kurus try to kill their cousins by many conspiracies and political intrigues. The Pandavas remain patient throughout all these and they try to come to a peaceful solution by all means.
It finally comes down to full scale war and the Pandavas make a last ditch effort to avoid the war. At that point, advisor of the blind king gives him the advice of rejecting only the eldest son to avoid the destructive war. (Point to be noted that the blind king isn't a bad person to say. He often feels sorry for the Pandavas and knows the right thing to do. But his affection for his eldest son makes him blind figuratively too). If he could only banish his oldest son who is the root of this conflict a destructive war could be avoided. He reminds the king of the history of one of the kings in his own dynasty.
There was one king long before him who had a similar dilemma. This king named Bharat had nine sons. He was a very qualified and a kind king to his citizens. But his sons turned out to be wicked. They took pleasure in tormenting the citizens. The king asked for advice from his ministers and they advised him to get rid of his sons. The king actually assasinated his own sons. He adopted a son and made him the king. He was a father. But as a king he was also the father of the citizens. Even after hearing this the blind king could not change his ways and that lead to the final war.
The point is that ideals are desirable. Heroes need to have that. People could then see that there can be something pure in this world. So, i commend this on one level. On the other hand, if Superman has to really be the ideal of hope he has to sometimes let go of a moral choice, if the immoral choice actually is on the higher ground.
In this specific scenario, its definitely wrong to step down. Say Superman steps down. Will the others too? If not, and Superman knows this will lead to deaths of billions, will Superman actively try to take down the heroes himself? Because if he doesn't, he would be responsible. You see. Superman has power. So, in order to stop the apocalypse he has to stop the heroes too. Since, they are active, it will lead to death of billions in the future. So, inaction is no solution.
Superman will try to work with the other heroes prepare for the endgame scenarios and fight. He has to fight anyway. The upcoming disaster or the heroes. Its a far better choice to fight alongside good people to avert the inevitable. Who knows? Together they could avert the inevitable. That is what hope means. Realistically speaking, Superman will try to save all twenty one in danger including the girl. If he could not save all of them, he isn't responsible as he tried. And if its an impossible choice, he has to choose the twenty.
Weight on the conscience is something he has to deal with. In Mahabharata the eldest of the Pandavas was very distraught after the war and wanted to leave aside the hard won kingdom. This after he tried everything within his power and more to avoid the war. Who had to fight when it was finally inevitable. He had to take help. And after that he took up the position of the king. It was a devastating war and leadership was needed to rebuild.
Now about the question of Superman not being able to save a number of lives because he is talking with friends. I don't have a clear idea. Even if Superman could know there are people in danger, he is neither omniscient nor omnipotent. He does not know everything. Nor does he have all power. He is not fully independent. Superman's senses have limits. His ability to process information has limits. His ability to predict the future has limits. His powers have limits. He isn't fully independent. To illustrate how is not fully independent say he stops a crime scene in North Korea. That could lead to increase in global tensions which can tilt countries more closer to war. What shall he do?
I think this can lead to a number of interesting scenarios. I have always thought the Superman is the thinking guy's superhero. I enjoy that.