You can take kahnclusions' word for it, or you can take Eugene Wigner's:
> I have known a great many intelligent people in my life. I knew Planck, von Laue and Heisenberg. Paul Dirac was my brother in law; Leo Szilard and Edward Teller have been among my closest friends; and Albert Einstein was a good friend, too. But none of them had a mind as quick and acute as Jancsi (John) von Neumann. I have often remarked this in the presence of those men and no one ever disputed. But Einstein's understanding was deeper even than von Neumann's. His mind was both more penetrating and more original than von Neumann's. And that is a very remarkable statement. Einstein took an extraordinary pleasure in invention. Two of his greatest inventions are the Special and General Theories of Relativity; and for all of Jancsi's brilliance, he never produced anything as original.
Neumann was a human calculator + encyclopedia in one. If there was ever intellectual olympics track and field, he would dominate the single sprint event.
What Einstein had was a deep curiosity, damn near super-human persistence, and some measure of an inventor's creativity. Even in mundane interactions, his curiosity stood out.
> I have known a great many intelligent people in my life. I knew Planck, von Laue and Heisenberg. Paul Dirac was my brother in law; Leo Szilard and Edward Teller have been among my closest friends; and Albert Einstein was a good friend, too. But none of them had a mind as quick and acute as Jancsi (John) von Neumann. I have often remarked this in the presence of those men and no one ever disputed. But Einstein's understanding was deeper even than von Neumann's. His mind was both more penetrating and more original than von Neumann's. And that is a very remarkable statement. Einstein took an extraordinary pleasure in invention. Two of his greatest inventions are the Special and General Theories of Relativity; and for all of Jancsi's brilliance, he never produced anything as original.