As a full stack dev with experience with both Angular and Rails, and recently been interviewing, I think Angular will serve you better over the next few years.
There is currently a focus on pushing the envelope with front-end UX, single page apps, etc. etc. I think a lot of the interesting work will be in that area. I suspect that over the next few years, the majority of back end work will continue to be pushed toward being APIs to serve the front-end javascript.
At the same time, having a server-side language in you toolbox is a good thing. But why rails? You already know javascript, to it seems to me the obvious path would be node.js. It is becoming extremely popular, and will allow you to leverage your existing knowledge of javascript.
Beyond everything else I've just said, I've recently started programming with node-webkit (I'm making an IDE) which further expands your horizons to installed apps to desktop environments.
Though there are a lot of haters out there, there is a huge future in Javascript, Rails is popular in certain circles, and it's a great language, but I wonder how popular it will be in another 5 years.
In terms of what's most attractive to an employer, it really depends on the company. What should matter more is where you see yourself in five years.. if you have no interest in backend coding, by all means focus on Angular, but if you want to branch out from front-end development, Rails will get you quite a bit farther.
Plus you will have the skills and knowledge of how to plug your front end design into the backend systems.
Both Rails and Angular are MVC frameworks but I suggest that Rails is easier for a beginner coder to learn, especially if you already have a high level of comfort with HTML, CSS and jQuery.