Good practice to return JSON from operationcontract in WCF

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C#

WCF

I am having an operationContract in WCF whose return type is an object and I need to send that object in JSON format to user. Now I have come across two ways of returning JSON data from my method. Please suggest which one is the good practice to adopt?; Does serializing the model as done in second way provides any additional benefits?

What I have tried:

The two ways of returning JSON data from my OperationContract are as followed:-
1)

[OperationContract]
        [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.WrappedRequest, ResponseFormat = WebMessageFormat.Json)]
        public Model1 GetData(string Id1, string Id2)
        {
            try
            {
                Model1 objModel  = new Model1();
                DataSet ds = new DataSet();
                BAL objBAL = new BAL();
                objModel  = objBAL.GetData(Id1, Id2);
                return objModel  
            }
            catch (FaultException ex)
            {
                // error handling code here
            }
        }



2)
 [OperationContract]
        [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.WrappedRequest, ResponseFormat = WebMessageFormat.Json)]
        public string GetData(string Id1, string Id2)
        {
            try
            {
                string json = string.Empty;
                Model1 objModel  = new Model1();
                DataSet ds = new DataSet();
                BAL objBAL = new BAL();
                objModel  = objBAL.GetData(Id1, Id2);
                json = new JavaScriptSerializer().Serialize(objModel);
                return json;
            }
            catch (FaultException ex)
            {
                // error handling code here
            }
        }