These are two great stories to compare! However, I would personally say that these two stories contain more evidence of differences than they do of similarities. Consider the following evidence. Firstly, although the protagonists of both stories are young man who find themselves out of step with their society, the reasons for this are very very different. Let us remember that Kreb is disillusioned and isolated because of the horrors he experienced whilst fighing in the war. What characterises his anti-heroic personality is the profound lack of attachment and the desire to avoid any involvement in life that is summarised in the following quote:
He did not want any consequences. He did not want any consequences ever again. He wanted to live along without consequences.
This quote more than any other speaks of the emotionally exhausted and desperate state of the mind of Krebs. He has suffered so much that he wishes to bow out of life and not have any attachments or involvements.
This of course stands in sharp contrast to Sammy, who makes his stand against Lengel precisely because of his desire to have attachments and to live life in a way that he desires. His decision to quit symbolises youthful idealism that inevitably comes into conflict with society and its values, and even though Sammy knows how difficult his life is going to be, he still makes this decision and choses not to return. Consider how Sammy describes Lengel and his own future at the end of the story:
His face was dark grey and his back stiff, as if he's just had an injection of iron, and my stomach kind of fell as I felt how hard the world was going to be to me hereafter.
Sammy has picked a very difficult path as he chooses to live a life that will be in conflict with society, but the key difference is he has chosen this life himself. Krebs stands outside of society, but he is a passive, weak character who has not made this active choice.
Thank you so much for your guidance :)