We added a preview of the JPEG-XL encoder to https://squoosh.app (and WebPv2) so you can try it with your own images.

In my experience, AVIF tends to outperform JXL in most web use-cases. However, for cases where the image should be really high quality (where the image is core content, like Flickr or Unsplash), the winner is less clear. Also, at those kinds of sizes, JPEG-XL's progressive rendering becomes an important factor.

But seriously, there's so much hype around these image formats, the best thing to do is to test it with your own images and your own eyes.