I had to move most of our apis/background-jobs to node after getting fed up with the concurrency issues that ruby had. This fixes that. Although I don't think it can compare with node/eventmachine on the performance front. But that's ok IMO in most situations.
I am thinking about moving most of our api/background tasks to ruby from node, and using node only for cases that require some sort of proxying - for example proxying an request to a private elasticsearch server after authenticating.
I'm sure the winners will depend on your needs. Do you need a full stack or not?
For me, it's either Django or Flask for Python depending on how much of a framework I want to start with. Both are mature projects in active development with a wide user base for assistance.
Right now I'm sort of in the Java world so Play! is my framework of choice.
Django is already well established, and so is flask.
If that sort of thing floats your boat, you should check out Yesod as well (Haskell).
Therefore, front end frameworks like Ember, Backbone and Angular are what I hope to see spread in web development.