return HttpResponseMessage with ObjectContent Json Type

public async Task<HttpResponseMessage> Register(AllenRegistration model){}

1.Will return 400 Error 
  return Request.CreateResponse(HttpStatusCode.BadRequest);
2.Will return Json Type like   {"return1":"A","returnB"L:"B"}
return new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new ObjectContent<object>(new
                {
                    return1="A",
                    return2="B"
                }, Configuration.Formatters.JsonFormatter)
            };
        }
}