Going by my experience, if you are using Websockets, choosing Phoenix would be a really good choice. There's a lot of work that's gone into transport adapters in Phoenix (websockets and recently polling support was also added). @peregrine and @chris_mccord did a lot of work as far as I can recall. I've been noticing that @JoseValim has joined in too.

That said, I would love some websockets stuff refactored out of Phoenix into a Plug so that it can be used even without Phoenix. I'm not sure about the amount of work that would require.