http://www.saruhanhotel.com/ was close to all the major "must-see" places (about 10 minutes away.) They even arranged for a pick-up at the Ataturk Airport, which was very convenient. The hotel itself was staffed by very friendly and helpful people.
Breakfast was served upstairs on the terrace, from where you could get a lovely view of the city and the Marmara Sea. There was a sports complex close by and it was fun to watch them playing soccer on the turf.