who according to you wins the bet?

I do not think either one really won the bet. What is true is that the young man has read and learned as much as he can and he discovers that the "things" that people cherish are meaningless, including the money that he once thought would be everything he wanted. The man who made the bet did not understand anything that the prisoner learned. They really both lost; there is no ending when we do not consider the feelings and considerations of others.