I just spent a week in Istanbul at the end of March. This was my first trip to Istanbul (and Turkey). IMHO you can not beat the location of the FS in Sultanahment for a first time tourist. Speaking for myself I’d find it difficult to sit around the pool for longer than about 10 minutes when the worlds 5th largest city is out there for me to explore for the first time… even in August heat. The FS in Sultanahment does have a fairly large amount of public space to relax, have a drink, etc… just no pool.

I spent only 1 night at the FS Sultanahment and 6 nights at the Park Hyatt Istanbul due to cost considerations. Almost everything we did during our one week stay would have been more convenient had we stayed at the FS Sultanahment and I think this would also hold true vs the FS Bosporus as I think it is even slightly farther out than the PH. If I had already done the major sites on previous trips and just wanted to hang out in Istanbul for whatever reason, then I’d be more inclined to go for the more resort like property on the Bosporus (actually I’d stay at the Park Hyatt again as I loved it). If you are looking for some relax time I’d split the stay 3 in S and 2 in B.

FWIW I was not overly impressed with my deluxe room at the FS Sultanahment. It was certainly well kept, quiet, had a spacious bathroom a comfy bed and the rest… but still pretty ordinary for a luxury hotel IMHO (rooms have compact fluorescent lights, yuck). Everything else about the hotel is very nice, with location being the real win for a first time tourist. BTW, the rooms at the Park Hyatt were orders of magnitude nicer than the FS Sultanahment (and from what I can tell from photos on FS website, also the FS Bosporus). The Park Hyatt rooms also feature fantastic dimmable halogen lighting and not a single compact fluorescent in sight.