The most significant difference between sweet onions and regular onions is the taste. Sweet onions are milder than regular onions and have a slightly sweet flavor. They are perfect for dishes where you want the onion to be noticeable but not overpowering, like French Onion soup. Regular onions are sharper and have a more intense flavor. They are best used in dishes where you want the onion to be the star of the show, like a burger or pizza.