Basically I was hoping to do a deep dive into one tech. Like I said, I've been already playing with the mentioned 3 tech but neither an expert nor know enough about them. By working on my side project I would like to see myself move into a promising tech that will help me stay in the job market. So if you were me, what would you do?
I think if you lean towards system programming at Google, go with Go. If you want to do web dev, either Rails or Node.js would suffice. If you want to do both backend and frontend, familiarity in javascript, go with Node.js. Rails libraries are more mature, but most new interesting libraries seem to be in javascript.
It's my 10x better test. In general, I think all three are good to know, and each are good at what it does. Ruby is in the 'everything is an object' world, and does it well. It optimizes for programmer speed, rather than execution speed.
Node.js is like being dragged halfway to lisp and functional programming. Learned a lot here, but having callbacks is almost like having to program with continuations all the time.
Go is for systems programming, and it's got its own take at concurrent programming. It's worth looking into.
Either way, just start at one, and eventually do side projects in the others. Can't hurt to know them all.