Another vote for Meteor. To me, it looks the most promising for a full JS stack framework for prototyping and rapid development. As with all things though, wha

Another vote for Meteor. To me, it looks the most promising for a full JS stack framework for prototyping and rapid development. As with all things though, what's new and edge may not necessarily scale or be supported in the long-term so caveat emptor (I think we need a developer specific latin phrase here). Once a service/site has become successful, key considerations such as community, active development, roadmaps, extendability etc. become paramount. For those, you really can't beat some of the time-tested communities around PHP (Symfony/Cake), Python (Django/Flask/Bottle), Ruby (Rails/Sinatra) and Java (Spring). I'd say that Node.js is entering this space from the backend perspective, but the front-end JS frameworks are an open battlefield right now (which is awesome, just fragile).