I am a big fan of AngularJS and an even bigger fan of ROR. Rails and AngularJS both have some similar concepts that helps a developer to understand the Front-end and Backend requirement in a better way to build a more stable and scalable product. Here are my 5 reasons from experience, why these 2 are complimentary and a good choice together.
1. MVC Framework
Rails and AngularJS both are based on MVC framework. You can use Rails as a server side MVC and AngularJS as a client side MVC, through this you will get much more freedom to play with your data. By using Rails as back-end you can easily create REST API with CRUD operations and You can write your front-end in AngularJS accessing a RESTful server API. Later in future if you want to change your backend with any reason (I know it's no small thing to rewrite a whole back-end; but), it's much easier when you don't need to worry about the UI.
2. Option to Pick Best
Every framework is special and each one's are best in several things. We can also get the option to pick best from both frameworks and used it our application. Rails is the best in handling routing, helpers and primary application logic. Whereas, AngularJS is best in handle client-side interactions, ajax request, dynamic binding and presentation logic's. By using both approaches in an efficient manner, we can stay away from many headaches caused by Rails remote linking, endless arbitrary JQuery listeners and Angular routing etc.
3. DRY and Write Less Code
Both Framework have some good feature which make developer Happy. Rails is based on DRY principle which means Don’t repeat yourself. In rails any method or class which is used more than one places, can be called from anywhere i.e you define or write once, and use it as many times you want. Using efficient “data-binding” provided in AngularJS the developer can achieve the zen of “Write-Less-Code”.
Testing is an integral part of any software. In web application both the front-end and back-end testing are required. Rails+AngularJS provides us with excellent options for both of the testing. For your back-end Rails provide both types of testing TDD and BDD. AngularJS was written from the ground up to be testable. You can use "Karma" and "Jasmine" to test your front-end.
5. Good Community Support
Last, but far from least, is the Rails and AngularJS community. There's no shortage of resources for learning Rails and AngularJS. Huge support from Ruby on Rails Programmers who keep up to date by their research papers and blogs. It also have so many platform where you can ask your questions. On the other hand AngularJS that itself is developed by Google, also has number of dedicated communities ready to help anytime.