IMO there is not a single magic sound but there are a few vocals that I have more success with than others. You will need to get out and try different sounds to see what works best for you, night by night. On one night they might respond to one sound, no response at all to that sound the next night. Who knows what trips their trigger on any given night?
The call makers are constantly coming out with the new "greatest ever, must have, click here to purchase" sounds but IMO just basic howls and a pup distress are about all that you really need. Your set up is just as important. If they see or smell you it won't matter what sound that you are using. Put yourself as close to them as you can and don't over call.