Here's a true fact about programming:

Following the herd means that there's a better chance that someone will have already solved any given problem you encounter and released documentation or a drop-in implementation.

I like the idea of Django/Bottle/etc. because I use Python for a lot of my non-web stuff. But RoR has a bigger and more active population. Unless there's something specific to your situation which changes this equation, you'll save yourself time and effort if you go with the more mainstream option.