I've used RoR and Node. RoR has a bigger community, so you're likely to find answers faster, and probably provides better job security. You may want to try Ruby/Sinatra, which I prefer over Rails. When you're learning, Sinatra forces you to develop more yourself, so you're more likely to understand what's going on. It's less "magical" than Rails.

Node is better for streaming/real-time applications. You can build any type of web app with it, but it's best known for chat/real-time stuff.

That said, I actually love Node and plan to use it as much as possible, over Ruby/Rails/Sinatra.