You can't go wrong with any of them. I think Django has a slight edge by having a slower release cycle. I find it a desirable quality in a development framework.

While the number of man-months spent developing Rails is an order of magnitude greater than that spent developing Django, is it really that much better for the bottom line?

Most of the early efforts spent on Rails were to make the infrastructure and community more mature. Even the brilliant DHH was a PHP developer before he started Rails.

On the other hand, Django benefited a lot from Python's maturity.