go through the tutorial for both django and RoR and see how you feel about each one.
I will be using a hosting service so the ease of use in implementation is also a big issue, not just the framework itself.
Personally, I chose django, but only because I was a python programmer before ror and django took off. If I were to do it again, I might look seriously at Pylons, as I consistently read good things about it.
I deployed a smallish rails app on Dreamhost in about 5 minutes last night. My previous attempt to deploy on a stock SuSE/apache2 server took a few days of fairly dedicated prodding.
I learned more from launching a demo application in both (I used a blog and a poll as an example) than I could have by asking other people. I found what suited my tastes.