ShortPixel Adaptive Images vs. Autoptimize's "Optimize images" option
Which one should I use? ShortPixel Adaptive Images (SPAI) or the option "Optimize images on the fly and serve them from Shortpixel's global CDN" on Autoptimize?
Both use the same ShortPixel service, the ShortPixel Adaptive Images API, and both can deliver optimized and "next-gen" images (e.g. WebP), but there are differences.
Autoptimize uses a combination of a server- and client-based approach: for image optimization the image URLs are changed server-side with the CDN URL, but client-side logic is only implemented if lazy-loading and/or WebP delivery are active.
ShortPixel Adaptive Images tries to determine in the browser what is the resolution of the image for the particular device resulting in better sized images in most cases, but for this purpose it has to lazy-load the images which could cause incompatibilities with some plugins and themes (here's how you can troubleshoot that).
In simple words, ShortPixel Adaptive Images is like Autoptimize's image optimization with a few more useful features, like serving scaled images. Our advice is to try ShortPixel Adaptive Images if you don't have Autoptimize yet, and if you see any incompatibility try to install Autoptimize and use the image optimization service in there. If you already have Autoptimize you can start with that, but if you want perfectly sized images for each device being requested try out Shortpixel Adaptive Images (deactivating image optimization in Autoptimize).