Use whatever you know best. This decisions tend not to be so important. If your app becomes real big you will end up replacing most of your code anyway. The most important thing is to build and launch as fast as possible.

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.

Is one of the goals for this project to learn a new language/framework or purely to get the project up and running? If it is the latter I would suggest sticking with what you know (PHP) and this way you will get the project off the ground quicker. If it is part of your goals then first I would suggest looking into whether you want to deploy on something like the google app engine or heroku. This might help you decide if you want to go down the Ruby or Python route.

Off question, but I am working on a very similar idea (only in my head for now). Hit me up if you would like to connect. My email is in my profile.

Sent you an email. Looking forward for your reply.

Smalltalk