In "The Most Dangerous Game", which character's internal conflicts contribute most to the story's action and effect on the reader?

The two main characters are Zaroff and Rainsford. Zaroff has no internal conflicts. He is single-minded. He believes that he is a hunter and that role dictates his life. He has no ethical problem with hunting humans or any other animal. For Zaroff, there is nothing morally conflicting.

While on the yacht, Rainsford has no real conflicts either. He tells Whitney that there are two kinds of people: "the hunters and the huntees."  At this point, he is not as radical as Zaroff, but he expresses the same ideology that Zaroff follows. If Rainsford is hunting a jaguar, he doesn't care how the jaguar feels. He is the hunter and the jaguar is the prey.

However, when Rainsford learns that Zaroff hunts humans, he is appalled and, hopefully, so is the reader. Rainsford would never hunt humans himself, so he has an ethical disagreement with Zaroff. Then, Rainsford becomes Zaroff's prey and he (Rainsford) has an entirely new appreciation for the fear and anguish of being preyed upon. The reader follows Rainsford's internal conflicts of learning what it's like to be preyed upon while struggling to survive.

The narrator never says that Rainsford might now sympathize with the jaguar or some other prey. But Rainsford clearly learns what it is like to be the "huntee." The end of the story is not absolutely clear, but the final line suggests that he kills Zaroff and then sleeps in Zaroff's bed, effectively taking Zaroff's place and symbolically becoming Zaroff. This leaves the reader wondering if he will stay and be the next Zaroff. If this is the case, Rainsford will ignore any internal conflict about hunting, just as Zaroff had. A more optimistic interpretation of the ending is that Rainsford sleeps in Zaroff's bed, gets up the next morning, leaves the island, and vows never to hunt again. The ending leaves the reader wondering what will become of Rainsford.