Let us say if familiarity with a technology stack is not a prerequisite which technology stack will be your choice for a web application. This application needs to integrate with external websites and also needs to be written using minimal investment of money. The application will be used by thousands of users per day. What will your choice?
I have been doing web since 6 months after the first page was developed I have seen every stack from CGI/C to ROR and for me personally I have not used a better stack than an HTML/JS front end communicating via REST backend. I personally used Java to provide my REST services, but have recently switched over to Clojure. The back end language is not as important as the architecture of the application. I think HTML apps that communicate with REST backends is the cleanest architecture the web has seen for web apps.