Three Sisters Island is your best bet.

Of the three islands near the American Falls (Goat, Luna, Three Sisters), Three Sisters offers the most secluded spot for a quiet view of the rapids. It’s the smallest and farthest out, so fewer tourists bother to walk all the way.

Goat Island is the main hub — crowded, noisy, with lots of paths. Luna Island gives you a close view of Bridal Veil Falls, not the rapids, and it’s still pretty busy. Three Sisters, on the other hand, is a series of tiny connected islands that jut right into the upper rapids. You can find a rock to sit on, hear nothing but water, and watch the current rip past.

If you meant different islands (like in the Thousand Islands or somewhere else), the logic still applies: pick the smallest and hardest-to-reach one. That’s where the quiet is.