I did a little of eval work on modern codecs as someone who takes photos with a mirrorless and wants them to look like photos taken with a mirrorless. I came to the conclusion that WebP is better than JPEG but that AVIF isn't really better than those.
AVIF is very strong for high compression with low quality, like if you want a huge splash image for your blog that people aren't supposed to look at closely it's absolutely amazing. It's a still encoder derived from a video encoder and... video can look great even if individual frames aren't so good. For instance, individual frames of VHS video are atrocious but if you sit back and enjoy the movie, particularly with a home theater that supports Dolby Pro Logic II it's just fine.
Whenever I say this people point me to a demo with the image of a race car which is superficially impressive but if you look close you can see that AVIF replaces a highlight with something that looks superficially similar but is... completely different. I'm just so happy the industry managed to pressure Google into doing the right thing and supporting JPEG XL which is a truly superior next generation still image format.