What's the difference between DataContractJsonSerializer and JavaScriptSerializer?
The .NET Framework ships with System.Runtime.Serialization.Json.DataContractJsonSerializer and System.Web.Script.Serialization.JavaScriptSerializer, both of which de/serialize JSON. How do I know when to choose one of these types over the other? MSDN doesn't make it clear what their relative advantages are.
We have several projects that consume or emit JSON, and the class selected for each thus far has depended on the opinion of the primary dev on each project. Some are simple, two have complex logic regarding producing managed types from JSON (the types do not map closely to the streams) but don't have any emphasis on speed, one requires speed. None interact with WCF, at least as of now.
While I'm interested in alternative libraries, I am hoping that somebody might have an answer to my question too.
Answer
The DataContractJsonSerializer is intended for use with WCF client applications where the serialized types are typically POCO classes with the DataContract attribute applied to them. No DataContract, no serialization. The mapping mechanism of WCF makes the sending and receiving very simple, but only if your platform is homogeneous. If you start mixing in different toolsets, your program might go sideways.
The JavaScriptSerializer can serialize any type, including anonymous types (one way), and does so in a more conformant way. You lose the "automagic" of WCF, but you gain more integration options.
As you can see by the comments, there are a lot of options out there for AJAX serialization, and to address your speed vs. maintainability questions, it might be worth investigating them to find a solution that meets the needs of all the teams, to reduce maintainability issues in the long term as everybody does things their own way.
2014-04-07 UPDATE: I suggest using JSON.NET if you can. See http://james.newtonking.com/json Feature Comparison for a review of the 3 libraries considered in this question.
2015-05-26 UPDATE: If your company requires the use of commercially licensable products, or you need every last bit of performance, you may also want to check out https://servicestack.net/.