As a both Django and Rails developer I suggest you to choose Ruby on Rails.
Rails pluses:
- Has a nice asset pipeline (automatic conversion of CoffeeScript, Sass, Haml, Jbuilder, etc) and concatenation + mignifying.
- Really configurable database migration with a nice DSL. (Django has South which auto generates migration files, but It isn't just as easy to change them)
- Rake tasks (Django also has management commands, but It's easier in using rake)
- multiple environments (development, production, testing), being able to store different configurations (Django does not have this, you can achieve this using some hacks)
- Railscasts.com (great screencasts by Ryan Bates)
- Better release circle, as long as I know in Django didn't appear many features since 1.0 (mostly bug fixes and Python 2.x deprecation warnings)
- more OOP than Django, it really follows MVC pattern, Django is a MVT (Model View Template framework)
- More libraries and more complex and configurable than django libraries. Most Django libraries handling authentication stick on default User class, so it's difficult to subclass it if you require custom fields.
- Model hooks and scopes (I know django has model hooks but they are built using Django signals, not using nice DSL as in Rails)
- Concerns inclusions which guides you to a clean coding style.
- Controller before_filters (very useful when you want to run a filter before multiple actions, eg: check if user is logged in), I know it can also be done using Django middlewares.
Django pluses:
- Django admin (Rails also has a few plugins which try to implement this, but django's is built in and also well documented in their official docs)
- Django built in authentication system (Rails comes with devise library and other alternatives, which is great but not built in)
- Easier to learn (Django follows Python's Zen, "Explicit is better than implicit.", all classes or methods you use must be imported, Rails pollutes global namespace with all classes and namespaces imported from libraries when Gemfile is parsed). It is easier to learn which module each class comes from and it helps you a lot at debugging if you are a begginer.
- Django middleware (you)
- Form based validation (each model can be validated using form class, another minus for Rails is that there was some security vulnerabilities targeting mass assignment on Models)