You might want to consider LocalBroadcastManager.sendBroadcastSync() http://developer.android.com/reference/android/support/v4/content/LocalBroadcastManager.html#sendBroadcastSync(android.content.Intent)
If your activities and services are in the same process then it is is better to use LBM since it is faster and more secure. And it gives you the option of sending a broadcast 'sync' which means it is handled immediately, so it would probably qualify as 'fastest', even though messages/handler are otherwise faster then intents/receivers.