I used Rails for 4 years, then Django for 2 years, then back to Rails (now for another year).

Programming with Ruby and Rails is like a breath of fresh air compared to Django. Working with Django was just so painful and awkward (especially if you are trying to write tests for things). I used to have a laundry list of a couple of pages worth of things that I hated about Python and Django when compared to Ruby and Rails, but I can't seem to find it right now.