When saving images for the web, we need to strike a balance between file size and quality. For most images, the above settings when used in Adobe Photoshop CS5 will yield excellent quality within minimal file sizes. If you select "optimized" you may get a slightly smaller file size. Resist the temptation. We know that progressive JPEGs (while bigger) will appear to load faster to the user.
Let us show you proven strategies to optimize your Shopify business: