What Are The Best Programming Languages for a Large-Scale Project?

The company I work for is upgrading its systems from .NET (ug), and they want to know what languages to switch to. They have a massive user database and some complex algorithms that need to be run constantly. They want a site that is self-contained in that data can be collected and displayed in real time to admins. Right now our CTO is leaning heavily on Ruby on Rails, is this a good idea or a bad idea for such a complex project?

I apologize if this is vague, corporate rules and whatnot forbid me from going too much into details.