Just completed a great stay the the Grand Hyatt Istanbul. We had booked a 3 day award stay, and though I'm a lowly Platinum, they upgraded me to a room on the club floor and gave us (family of 4) access to the lounge including free breakfast.
Hotel is located in a nice area in Taksim. Took us about 30 minutes to get to the Old City by public transportation. Breakfast at the lounge was good (cold buffet with some hot items that you could order such as eggs, meats, etc.). Used Istanbul Airport Transfer for easy transportation to/from the airport. Booked online and paid the driver.