Images are usually the heaviest thing on a page, so the format you serve them in matters more than almost any other optimization. The two modern options — WebP and AVIF — both beat JPEG and PNG, but they’re not interchangeable, and picking wrong either wastes bytes or wastes your time.
WebP is the safe default
WebP is about 25–35% smaller than JPEG at the same quality, supports transparency, and works in every browser people actually use. Converting a library to WebP is the single biggest image win for most sites, and it’s low-risk.
AVIF goes further, with tradeoffs
AVIF is often 50% smaller than JPEG, with better detail in gradients and dark areas. But encoding is slow and CPU-heavy, so generating it on the fly can hurt the server, and very old browsers don’t support it. For photography-heavy sites where every kilobyte counts, AVIF is worth it. For a typical business site, the extra savings over WebP often aren’t.
The pragmatic answer is to serve both with a fallback: AVIF if the browser takes it, WebP if not, original as a last resort. A <picture> element handles this, and most image plugins or a CDN like Cloudflare can do it automatically.
Don’t agonize over the choice. Convert to WebP today for an immediate win, and add AVIF later if your images are the kind where the extra compression actually shows.