See, I think the label transcends where you're born, but that being an Italian filmmaker means making a body of work representative to the style or culture or tone or attitude or setting or all of the above of your country. Argento and Bertolucci are very much Italian filmmakers (fuck Fellini), but I always have felt that Leone was an Italian that made American films.
If the argument is that, of all directors simply born in Italy, who is better, then Leone wins hands down.