Why does Eugene feel he got the better end of the deal with Vincent?

Eugene feels he got the better end of the deal with Vincent because Vincent lent him his dream, which was a chance to live a life he otherwise could not have. In the world of GATTACA, where genetic identity determines social class and opportunities, Eugene, who had been labeled as genetically inferior, found a sense of purpose and fulfillment through Vincent’s determination to reach for his aspirations. By allowing Vincent to assume his identity, Eugene not only enabled Vincent to pursue his goals but also contributed to the realization of dreams that seemed unattainable for someone like him.

This transfer of identity represents a profound connection between the two characters; Eugene’s willingness to sacrifice his own place in society for Vincent's ambitions illustrates an act of deep trust and camaraderie. It also reflects the broader theme of the film regarding identity and the inherent value of human spirit over genetic predisposition.