Do you mean with the parent fit extension or out of the box? I haven't done a in-depth comparison or the two libraries, but they have done a comparison here: https://github.com/verlok/vanilla-lazyload#vanilla-lazyload-vs-lazysizes But I don't think it is up-to-date as I do think lazysizes can lazy load background images as well. Vanilla lazyload seems to be a bit more lightweight though.