People frequently ask us about our take on ESRI’s RESTful APIs in the context of Web ADF. Basically, the RESTful APIs are an important and needed technology. They also aren’t a cure-all, and sometimes Web ADF is the right path (despite its flaws, there are lots of organizations satisfied and successful with Web ADF). We consider REST and Web ADF to be complementary technologies that we envision many folks will choose to run in parallel.
I like the following analogy:
I have five deliveries for you to make. Which of the following two vehicles is better?
Folks that don’t suffer the unfortunate predilection to gravitate permanently to a black and white answer might observe that it depends. If the deliveries consist of envelopes within a ten block radius, the small delivery van is the right choice. On the other hand, if there is two hundred miles between deliveries of heavy crates, then you’re going to want the rig. Which vehicle is better for deliveries? It depends.
Now we can be more vocal about this topic. It isn't about categorically picking one or the other. ESRI's RESTful APIs and Web ADF both have their place. The right choice depends on the nature of your app and likely evolution of that app.