Start with the content
Photographs usually suit JPEG, WebP or AVIF. Logos, screenshots and graphics with transparency often suit PNG or WebP. Keep artwork as SVG when the destination accepts vectors and the file is trusted.
Protect transparency and animation
JPEG cannot store transparency. A still-image conversion also cannot preserve GIF or animated WebP motion. Decide whether those properties matter before comparing file sizes.
Plan for compatibility
JPEG and PNG remain the broadest choices. WebP is widely supported in modern environments. AVIF can be smaller but should be tested in the exact browser, CMS, editor or delivery chain that will consume it.
Try the related local tools
This guide describes format behaviour and product capability, not a guarantee for every source image or third-party workflow. Keep your original files and verify important exports.