Github pages can only run builds of plain jekyll sites with no plugins. Netlify will work for pretty much any static site generator (right now we support ruby, node and python).

You can also trigger new builds without pushing to Git (essential for pages like https://www.staticgen.com that grabs data from somewhere else than the Github repo).

Apart from that there's hosting features like:

SSL for custom domains

Redirects

Rewrite rules

Fine grained header control

Lossless image compression

Automatically moves asset to content addressable URLs on a cookie-less domain with far-future expires headers

There's a few more things in the works as well.