Choosing an image format is mostly about balancing compatibility, file size, transparency and visual quality. There is no single format that is best for every image.
JPG for photographs
JPG is widely supported and normally works well for photographs. It uses lossy compression, which means repeated saving or very low quality settings can remove detail.
PNG for transparency and crisp graphics
PNG is useful for graphics, screenshots and images that need transparent areas. It is lossless, but photographic PNG files can be much larger than JPG or WebP.
WebP for efficient web delivery
WebP can provide small files and supports modern web use cases, including transparency. Compatibility is now broad in modern browsers, although some older apps and upload systems may still expect JPG or PNG.
Convert only when needed
Changing formats does not create missing image detail. Keep the original file and convert a copy for the destination that requires it.