A little bit of background: I learned Django first. Then I learned Rails via Code School, and flirted with building my app with Rails instead of Django. I saw the asset pipeline specifically as a Rails advantage over Django (I write Emblem, indented Sass, and CoffeeScript whenever I can avoid HTML/Handlebars, CSS, and JS). Also, building JSON APIs with Rails has better out-of-the-box support than it does in Django.

I always felt Rails' model layer is clunky compared to Django's. What is the definitive representation of my model? The validations in SomeModel < ActiveRecord::Base or what's automatically generated in schema.rb when I run migrations via Rake? In Django everything, including migrations (in simple cases), is derived from the classes in models.py. But I thought it would be worth it to persevere, due to the above-mentioned advantages.

Then I realized I could (and should) compile assets via Ember-CLI, and Django Rest Framework is just a pip install away. So the two main advantages of Rails disappeared, and switching back to Django became, for me, a no-brainer.

Edit: I also prefer Django's less magical approach. This may seem ironic given my love of Ember, but Ember's magic is easier for me to understand than that of Rails.

I am also a Rails dev, but one feature I think Django really got right that is head and shoulders above Rails are Form Objects (https://docs.djangoproject.com/en/1.9/topics/forms/). Rails' attr_accessible stuff and even strong_parameters really pales in comparison.