I've read through https://github.com/apotonick/roar and it seems like a lot of thought has been put into ROAR. But in the context of a fairly standard Rails-powered JSON API that uses jbuilder, I'm still not able to immediately see what benefits ROAR provides.
What am I missing?
Within a Rails project, you should do as much as possible to stick with the built-in solution, but outside a choice is mandatory. Personally one aspect that I love about ROAR is the versioning for the API.
There is one good post I like that might help you: http://devblog.reverb.com/post/47197560134/hal-siren-rabl-roar-garner-building-hypermedia
It might not be an straight answer, but it explains the problems you should be aware of when choosing a JSON API generator.