Lossless was not a focus point for AVIF. There JPEG XL wins hands down, with something like 50 % difference. Also, AVIF can only do up to 12 bit lossless, whereas photography workflows benefit from 14+ bits.

On lossy JPEG XL wins by 17%: https://twitter.com/jonsneyers/status/1532771586381688833

"Overall for lossy, for the same visual quality, JPEG XL is ~17% smaller than AVIF, which is ~17% smaller than WebP, which is ~17% smaller than JPEG."