[wriq]

There isn't a 'Best'. Getting a language & framework that will work for you is a personal thing. Just look at what's available (Rails/Play/Django/Node/etc) and implement a small but non trivial web app that has some similarities to what you're planning on building and see what you like the most. Ideally you will spend a bit of time researching on how to do something and you'll get an idea of what that language/framework's community is like.

Or just build it in PHP using Cake since if that's what you know the best you'll likely get it done faster. That way you can focus on the product instead of the stack, which in my opinion is more important.