JXL is the best image codec we have so far and it’s not even close. I did a breakdown on some of its benefits here. JXL can losslessly convert PNG, JPG, and GIF into itself, and can losslessly send them back the other way too. The main downside is that Google has been blocking its adoption by keeping support out of Chromium in favor of pushing AVIF, which started a chicken and egg problem of no one wanting to use it until everyone else started using it too. If you want to be an early adopter you can feel free to use JXL, but just know that 3rd party software support is still maturing.

Something you might find interesting is that the original JPEG is such a badass format that they’ve taken a lot of their findings from JXL and made a badass JPEG encoder with it named jpegli. Oddly, jpegli-based JPEGs are not yet able to be losslessly-compressed into JXL files, per this issue - hopefully that will be fixed at some point.

Jpg at 70% will lose a significant amount of detail. It is a “lossy” format, you cant judt compress data for nothing.

AVIF is significantly more efficient than jpeg, so it loses less image data for higher compression (smaller file sizes).

JXL supports both lossy and lossless compression, and is supposed to be more efficient yet over AVIF. However it’s got proprietary all over it because Google et al. For thst alone I would shy away from JXL and go AVIF.