Priority Hints is the more common of the two in our index: it runs on 22,246 websites against 296 for Autoptimize, and 178 sites use both. Counts come from real scans, not vendor claims.
Autoptimize is a WordPress plugin that optimises website performance by aggregating, minifying, and compressing HTML, CSS, and JavaScript files.
Priority Hints exposes a mechanism for developers to signal a relative priority for browsers to consider when fetching resources.
178 sites run both Autoptimize and Priority Hints. That is 60% of the sites using Autoptimize, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.