I prefer the Adlon, but it probably is too European for many Americans (does not look like a Marriott). Its location right at the Brandenburg Gate is one of a kind. It has understated elegance and charm.

The others mentioned may be just fine, as well. But the Adlon would be my choice if money is less of an object. I have stayed there twice (2001/2003). This year I will be staying elsewhere due to the appreciation of the Euro (and paying US 165 rather than 340).