What is the best quote in "The Most Dangerous Game" that indicates that Rainsford is actually intelligent?
Oh, there are so many! I've listed a few here with brief explanations. Overall, though, we must see that Rainsford success in defeating the General points to his overall intelligence and skill.
Rainsford remembered the shots. They had come from the right, and doggedly he swam in that direction, swimming with slow, deliberate strokes, conserving his strength.
Here he is in a dangerous situation, but he is intelligent enough to stay calm and use clues from his experience to lead him to safety.
"I've read your book about hunting snow leopards in Tibet, you see," explained the man. "I am General Zaroff."
This tells us that Rainsford has published a book, showing him educated and intelligent.
Rainsford's second thought was even more terrible. It sent a shudder of cold horror through his whole being. Why had the general smiled? Why had he turned back? Rainsford did not want to believe what his reason told him was true, but the truth was as evident as the sun that had by now pushed through the morning mists. The general was playing with him! The general was saving him for another day's sport!
Here we see Rainsford evaluating the situation and the person before him to come to a conclusion.
"I'll give him a trail to follow," muttered Rainsford, and he struck off from the rude path he had been following into the trackless wilderness.
And here, Rainsford is clearly making a strategy to win, not just trying to run and survive.