From my completely unscientific research on this topic - Its not the framework that matters, its the Language.
Its the age of tools - so keep trying newer things! Play around - node and web2py. We fall in love when we try new things.
In my case, I loved python more. I took the Django route. It does take some time to get acquainted with a framework and the community if you are new to web frameworks. 8 to 10 months of steep learning curve inside.
Here is a Quick checklist-
1. Do you like too much Magic? Rails is more magic than django.
2. Ask yourself - Do you love python or ruby as a language more? Its a team decision and access to developers available near your region.
I believe that, once you get solid grip over the language you will roll out your own and can bring-in changes in the core-framework.
Initially stick with one framework and dig inside!
3. I personally like the Django-python community more than Rails.
Folks with hardcore CS background + Having Linux backgrounds take the python route. YMMV.
4. You love Javascript? or Have a team with more front-end developers?
Its a good idea to first try out JS frameworks - node.js for server-side, Backbone and coffee-script. Check meteor.js. You may like it.
Finally I would love to hear - on what you're working on. Your profile doesn't read your email/contact.
The things that matter are: productivity, mature and stable framework code, and a solid set of libraries to pull for common tasks/integrations. These are the areas where Rails really shines and it's one of the reasons it has become so popular among early stage startups.
I agree with the parent on Ruby vs Python - just pick the path you're already more comfortable on.