The only comparison I can do is that Django Admin is built-in out of the box, so I use it on every Django project. Rails/Active Admin is not built-in out of the box so I've never used it and always built my own admin page.

It's super weird because Rails is known for convention over configuration and includes default packages for basically everything you might need EXCEPT auth and admin. Meanwhile Django removes a lot of the magic of Rails and lets you do it yourself, except for bundling auth and admin into the core product.