Maybe it’s just me, but having used both tools; graphQL-ruby is much simpler. There isn’t much to learn with graphQL-ruby, since the graphql spec is so elegant compared to jsonapi.
Fighting with the DSL, I mean cryptic errors, no instance variables to work with, and no straight forward way to extend the framework. I know it is possible to extend the framework, but it’s not very intuitive.
I've used Graphiti in a project; as it looked promising on the surface. But as my needs grew, I often found myself fighting with the DSL. It makes the easy things easy, and the hard things very painful and hard. This is a problem with any DSL heavy framework.
If you have a toy project, than try Graphiti. If you're solving real-world problems; stick with GraphQL.