JPEG-XL is not the best solution if you want small low-quality images, to reduce your costs for hosting some Web site. AVIF seems appropriate for that goal.

JPEG-XL seems to be the best solution for storing and distributing high-quality images. For myself, I want high-quality images, so JPEG-XL is what matters, both for new images and for compressing the old archives of JPEG images.

While I have my own Web server, it is for private use and not for commercial purposes, so I have no interest in using AVIF to achieve the smallest image sizes, but at a lower quality than I want.