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 stickin

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.