Elixir Lang
Elixir is the first in my list because it offers the most versatility to the wide range of challenges most web development projects have. With elegant solutions for addressing concurency, distrobution and even fault talerance it's a power house of solutions when paired with the phoenix framework. Elixir is not a silver bullet, rather more it's like buckshot. It's domain is just so wide and there is so much depth to the variety of solutions it can offer. For these reasons it remains my first go to when solving web domain challenges.