It's not about which is the best technology.
The barrier to entry for Node.js is next to nothing and the size of the ecosystem is incomparable to Elixir. Which means tons of companies will go with Node and feed back to the ecosystem and so on...
I have written a lot of Node services. Spent six years doing it. Gimme Java plz.
Assuming existing experience with JS / npm / async style. If you don't have that, I'm not sure which would be harder to start with. Given a little bit of experience with each, I'd actually lean towards elixir being a simple choice. Then again it depends on whether you're cool with training new devs in case of lack of elixir people.