I choose base on what type of project I'm working on. If there is a legacy project/library that I need to work with, I just go with whatever exists. just a no

I choose base on what type of project I'm working on. If there is a legacy project/library that I need to work with, I just go with whatever exists. just a normal web application? - ruby or php. building for enterprise? - whatever i feel like for jvm or .Net, but java or c# for the SDK heavy on rules? - prolog performance, small memory footprint - go/c++/c prototype, machine learning - python concurrency required - erlang/elixir, java/clojure