Haskell because of the type system. It's very satisfying to start a change in one location and have the compiler automatically tell you all the other places you

Haskell because of the type system. It's very satisfying to start a change in one location and have the compiler automatically tell you all the other places you need to modify across the whole project to finish the change and practically guarantee that it runs correctly. It's also great to not have to rely on human documentation to learn how to use a library. Looking at the type signatures is enough to learn how to use most of them. The type system also alleviates the need to write many tests. It's also efficient in that it runs very, very fast thanks to being compiled. The size of the compiled executables can be very small too, when you chose to use dynamic linking of the libraries. Choosing static linking comes with the advantage of not having to worry about installing library dependencies (beyond libc) where-ever you chose to run the resulting executables.