When you are using the brokered message in the Azure Service Bus, you can retrieve the body of the message with the call .GetBody. The code is simple:
var msg = subscription.Receive();
MyPayload payload = msg.GetBody<MyPayload>();
However, is there a way to retrieve the Body without explicitly knowing the class of the body object?
var msg = subscription.Receive();
Type bodyType = Type.GetType( msg.ContentType);
var payload = msg.GetBody<bodyType>();
If the intent is to only grab the message body regardless of the content you can get it as a stream.
Stream stream = message.GetBody<Stream>();
StreamReader reader = new StreamReader(stream);
string s = reader.ReadToEnd();