Between the two choices, Llewelyn Moss fits more squarely into the Aristotelian definition of the tragic hero. Aristotle defined a tragic hero as a figure who evokes pity because of some horrible misfortune. In all cases, the misfortune is brought on by some lapse in judgement or character flaw, most typically one of hubris. This is certainly the case with Llewelyn Moss. As a hardened Vietnam veteran, Moss has a great deal of faith in his level of strength and survival ability. This is evident from the first scene in which he is present, where the reader sees him exploring the desert completely under-provisioned.
Moss chooses to take the money for himself not because he believes that there will be no consequences but because he believes that he will be equal to any hardship that comes of his choice. He has not considered or even fathomed the existence of an unstoppable force of violence like Chigurh, who would haunt his steps every moment thereafter. It is this overconfidence that is his downfall.
Moss does not fit as well into Miller's definition of a tragic hero because he is not attempting to "claim his place" in society. Moss does not take the money because he believes that he deserves it or that it is his destiny. He is at least somewhat aware that he is acting opportunistically.