I spent three nights in Ada Hotel during a business trip in Istanbul. This is one of the best hotels I´ve ever been!
Firstly, I stayed in two different rooms. Both rooms were extremely tidy and clean. Rooms were extremely well equipped. Iron was an excellent surprise, especially since I was on a business trip. Toilets were very clean and luxurious. Even in some expensive hotels toilets can be "cheap" but in ADA Hotel it was the contrary. Hotel manager was very helpful and caring. Also the communication before arrival was extraordinary fluent.
Location is just perfect. After one block (100m walk) you are in the heart of Sultanhamet (Old City) where all the restaurants and people are. Also further transportation are available from there on. However the hotel itself is located in peaceful street and the noise from Old City does not disturb your sleeping.
Breakfast was very diverse and delicious. Taking into account that this is a small hotel run by few people the breakfast could be rated as 10++. Usually this versatile breakfast is available in hilto etc. And the roof terrace was extremely nice place to start your day while having breakfast.
All in all Ada Hotel is highly recommended!