The ocean generally considered the most peaceful is the Pacific Ocean.
This designation primarily stems from the experience of Ferdinand Magellan, who named it "Pacific" (meaning peaceful) due to the calm waters he encountered upon entering it after navigating the Strait of Magellan. While this was Magellan's specific experience at that time, and the Pacific Ocean certainly experiences storms and turbulent weather, the name has stuck, and it often conjures images of tranquility compared to the more tempestuous reputations of other oceans.
It's important to note that "peaceful" is a subjective term and can refer to both weather conditions and geopolitical stability. While the Pacific Ocean's name suggests calm waters, its actual conditions vary greatly depending on location and time of year. Similarly, the geopolitical landscape of the Pacific region is complex and ever-changing.
Therefore, while the Pacific Ocean is known as the "peaceful" ocean, this is more of a historical and nominal designation than a constant reflection of its actual state.