Use GitHub Pages if none of the benefits of Netlify above really matter to you.
If you have a public repo which uses Jekyll 3.9 or static HTML that you wrote by hand without templating.
You want to keep your hosting (GitHub Pages) close to your repo (GitHub), without introducing a separate account on Netlify.
GitHub Pages is especially nice if you have a ton of simple quickstart or demo projects that you just want to turn on and forget. No messing around in Netlify creating an app outside of GitHub. It gets messier to manage across GitHub and Netlify when you have over 10 sites like I do.
Having said that, Netlify does have a clean interface for viewing all the sites in your account and selecting one to update or view the deploy logs of.