We stayed in the Armada for 5 days and would recommend it as an excellent place to discover this city. The hotel is downhill from the main tourist attractions and is very close to the coast.
The breakfast buffet has an excellent array on offer, including fresh pastries and bread that are delivered from a bakery down the street; and also jams and preserves that the hotel produce themselves (look out for the jars of cherries fermenting on the terrace).
Sadly the dinner leaves a little to be desired, as it is something of a cliche menu. One highlight was that we told our waiter how much we enjoyed his Turkish coffee and the next day he had went to the spice market and picked some up for us!
Try and get a room with a view of the Hagia Sophia and the Blue Mosque.
Overall I would recommend the Armada as one of the best hotels in Istanbul.More