How to write a JSON string from .NET c# code for AJAX usage

Assume the variable name of the List is _List

System.Runtime.Serialization.Json.DataContractJsonSerializer serializer = new System.Runtime.Serialization.Json.DataContractJsonSerializer(_List.GetType());
System.IO.MemoryStream ms = new System.IO.MemoryStream();
serializer.WriteObject(ms, _List);
string json = Encoding.UTF8.GetString(ms.ToArray());

When to prefer JSON over XML?

Favor XML over JSON when any of these is true:

• You need message validation
• You're using XSLT
• Your messages include a lot of marked-up text
• You need to interoperate with environments that don't support JSON

Favor JSON over XML when all of these are true:

• Messages don't need to be validated, or validating their deserialization is simple
• You're not transforming messages, or transforming their deserialization is simple
• Your messages are mostly data, not marked-up text
• The messaging endpoints have good JSON tools