For backend I'd surely use Elixir/Phoenix, that's what I've used in the last 2 years, after ~9 years of Ruby/Rails. Elixir and Phoenix are fast to bootstrap, easy to use and deploy, even for complex scenarios (background jobs, websockets, key-value store, etc). Even for quick prototypes, I find Elixir/Phoenix a lot simpler than Ruby/Rails.
For frontend, thus JS, I'd use Vuejs. I switched to it after some year with React. It's a perfect compromise between React and Angular.
For frontend, thus JS, I'd use Vuejs. I switched to it after some year with React. It's a perfect compromise between React and Angular.