@abc.abstractmethod<EOL><INDENT>def choice(self, subscribers, message):<DEDENT>
Chooses which subscriber (from list) should recieve specified message.

@param subscribers: Collection of subscribed connections eligible to receive message. 
@type subscribers: C{list} of L{coilmq.server.StompConnection}

@param message: The message to be delivered. 
@type message: L{stompclient.frame.Frame}

@return: A selected subscriber from the list or None if no subscriber could be chosen (e.g. list is empty).
@rtype: L{coilmq.server.StompConnection}