Goebbles wasn't the only one admiring Hitler for his rhetorical talent.
Shortly after the Grande War he participated in anti-Bolshevik courses ("antibolschewistischen Aufklärungskursen") in Munich. Those courses had the expressed purposes of schooling their pupils rhetorically so they could spread anti-communist propaganda in the German Army.
Hitler was sent there because his superiors considered his oratory skills superior.
There is a discussion about whether Hitler was a covert agent ("V-Mann") under the commando of Karl Mayr to spy on communist and spartakist groups in Munich - Hitler himself stated in Mein Kampf that he was send to the German Worker's party ("Deutsche Arbeiterpartei") while assigned to Mayr unit (where the courses were held).
He participated in an discussion among DAP members which convinced the leader of the DAP to push Hitler to become a member.
A few years later (In the mean time he left the Army and made his income as public speaker) Hitler - now in the original NSDAP - was profiled by the New York Times.
He has the rare oratorical gift, at present unique in Germany, of spellbinding whole audiences regardless of politics and creed.
Hitler's strength is in the combination of his undeniable great gifts as an orator and organizer.
The New York Times, November 1922 http://query.nytimes.com/mem/archive-free/pdf?res=9A0CE0D91E3EEE3ABC4951DFB7678389639EDE
About a year later there was the failed coup which lead to a brief sting in prison and the writing of Mein Kampf.
In that he states
Everything I have accomplished I owe to persuasion
Theater and literary people like Tucholsky and Orwell could not dispute his rhetorical skills
The man does not really exist. He is only the noise that he produces.
("Den Mann gibt es gar nicht; er ist nur der Lärm, den er verursacht.")
Kurt Tucholsky - So verschieden ist es im menschlichen Leben!, Die Weltbühne
Hitler could not have succeeded against his many rivals if it had not been for the attraction of his own personality, which one can feel even in the clumsy writing of Mein Kampf, and which is no doubt overwhelming when one hears his speeches.
George Orwell, Review of Mein Kampf
An psychology evaluation also found that the most important reason for his rise was his talent for public speaking.
but he became for a while the most powerful individual in the world, primarily by the use of mass-intoxicating words.
OSS Pyschology review from 1943 - http://library2.lawschool.cornell.edu/oldsite/2007/donovan/hitler/Hitler-Section1.pdf