This answer is in the context of web development First I will say, in addition to the 3 that I will mention, you should have some level of experience with Java

This answer is in the context of web development First I will say, in addition to the 3 that I will mention, you should have some level of experience with Javascript, ES6 and Node. This is due to the pervasive nature of javascript in web development, mobile,realtime and client side build systems. That aside here are my choices: For highly scalable, fast and realtime web apps Elixir\Phoenix is my choice for its ruby like syntax, Erlang based language with a framework that has built in websocket support. Alternatively you can go with Golang or Scala\AKKA throwing in some Node for realtime capability. For medium scale web apps, rapid development, building MVPs. Python\Flask is my choice for an expressive dynamic language and flexible framework with big ecosystem of extensions. alternatively you can go with django, ruby\rails or php\Laravel For the enterprise, large project, large team, maintainable web apps C# and ASP.NET 5\Signalr is my choice for a dynamically compiled, statically typed, decently scalable with async capabilities framework including websocket support that runs on windows and linux Alternatively you can go with Java\Scala\Play