The short answer
Use JPG for photos when universal compatibility matters, PNG for transparency and sharp UI assets, WebP for most modern web images, AVIF when maximum compression is worth testing, GIF for simple legacy animation, and SVG for logos or icons that need to scale.
The best format depends on the destination. A product photo, app icon, scanned receipt, transparent logo, and animated sticker all need different conversion decisions.
When to convert images
Convert PNG to JPG when transparency is not needed and file size matters. Convert JPG to WebP when you want lighter product images or blog images. Convert AVIF to JPG when an older app cannot open a modern AVIF file.
Keep a high-quality original when possible, then export the smallest format that still looks clean in the place where the image will be used.
Quality checklist
Check transparency, text sharpness, color banding, and file size after conversion. For UI screenshots and graphics with text, PNG or WebP usually holds edges better than heavy JPG compression.
For SEO and page speed, the winning image is not the newest format by default. It is the smallest file that still renders correctly for the users and browsers you care about.