There are lots of solid choices, and as always it depends on what your problem is. If you want to have an easy time hiring, go with something popular like React, TypeScript, Python.
If you're willing to choose some excellent languages that are not going to be easy to hire for, I highly recommend http://elm-lang.org for frontend, and https://www.haskell.org for backend. Both of these scale incredibly well.
If you're willing to choose some excellent languages that are not going to be easy to hire for, I highly recommend http://elm-lang.org for frontend, and https://www.haskell.org for backend. Both of these scale incredibly well.