Unless you also see this as an opportunity to learn something new..in which case you could pick either ruby/rails or python/django (or any other ruby/rails framework)...or really anything, but those are probably your two best bet.

You also didn't talk about databases, but I think the same would apply. "Use whatever you know best", or pick something new if learning something new at this point (and on this project) is something you'd like to do.