In my experience, it's way easier to write client apps against a REST API. If you look at frameworks like Backbone, you can basically create models/collections

In my experience, it's way easier to write client apps against a REST API. If you look at frameworks like Backbone, you can basically create models/collections for a simple CRUD app just by adding some values to a declarative hash (URI, primary key, etc.). Because everything is so predictable, it's really easy to specify a default behavior. Granted, you could certainly do something similar with an RPC API, but I still think it would likely be harder to generalize.