jQuery Migrate is the more common of the two in our index: it runs on 5,740 websites against 29 for waitForImages, and 23 sites use both. Counts come from real scans, not vendor claims.
Query Migrate is a javascript library that allows you to preserve the compatibility of your jQuery code developed for versions of jQuery older than 1.9.
waitForImages is a lightweight, high-performance JavaScript library that simplifies the handling of image preloading events.
23 sites run both jQuery Migrate and waitForImages. That is 79% of the sites using waitForImages, 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.