From a location perspective, the Marriott, the Ritz, (and sort of the Westin) are very close to the old border between east and west, and gice excellent locations for going around Berlin. Taxis are cheap and plentiful, busses and trains are easy to deal with from there. But a lot of the central sights, Brandenburg gate, parliament, the holocuast memorial, most of the remaining parts of the walls and a lot of the museums are walking distance from there.
The Marriott and the Ritz are also very nice hotels, though I have never stayed at the Westin. Very close to the Marriott is the Mandala, a Design Hotel member which is another of my more preferred picks in Berlin