There is no single best format for every image. Choose according to what must survive: photographic detail, sharp text, transparency, animation or editable vector geometry. Then confirm that both the receiving application and your encoder support the choice. Compare actual outputs at equivalent dimensions and acceptable appearance rather than relying on a universal compression ranking.
Match the content to the format
JPEG is commonly useful for photographic delivery without transparency. PNG is lossless and can suit screenshots, diagrams and alpha transparency. WebP and AVIF can be useful delivery candidates when the workflow supports them. SVG represents vector graphics and is suitable for appropriate icons or drawings, not a magic compressor for embedded photographs.
Preserve the feature that matters
For a transparent logo, inspect partially transparent edges on the backgrounds where it will appear. For a screenshot, read the smallest important text. For a product photo, compare texture and labels. If motion is required, use an animation-capable workflow rather than a still-image export path.
Compare candidates under the same conditions
Illustrative experiment: export a photograph as JPEG and WebP at identical dimensions, then independently adjust quality until each version meets your requirements. Compare byte sizes only then. Equal quality numbers from different encoders are not equivalent measurements, and one format is not guaranteed to win on every image.
Check the destination and retain the source
A browser displaying a format does not prove an uploader accepts it or a browser encoder can create it. Keep a compatible fallback when the delivery system requires one. Preserve archival or editing originals separately, including TIFF or RAW files where appropriate to the workflow. The final decision should be based on accepted output and visible quality, not on treating older formats as automatically wrong.