After searching and checking for the other available .NET JSON serializer/de-serializer, i liked the way fastJSON & ServiceStack helped. Like DataContractResolver in DataContractSerializer(), fastJSON preserves the TYPE and ServiceStack is nice and clean at serialization time.
So for BOTH the libraries we no need to set [KnownType] attribute to the classes/types Or passing Type[] to the conversion method.
Here is a link about fastJSON in CodeProject: http://www.codeproject.com/Articles/159450/fastJSON
For ServiceStack : http://www.servicestack.net/
And also I have checked some other articles about the .NET JSON serializer's benchmark. Here I have listed only 2 of them:
1). http://theburningmonk.com/2012/11/json-serializers-benchmark-updated-including-mongodb-driver/ 2). http://www.servicestack.net/benchmarks/