Re: Cairo or Istanbul
Istanbul is much nicer as it has hills all around. You should visit Esentepe as well and see Bosphorus bridge from hill top, then go down in car. Its a zig zag road. See Sultanahmet, Topkapi museum, Haya Sofia, Laleli, Aksarai, Grand bazar and many shops around. Big shopping malls like Akmerkez, Galleria, etc. Have amazing sea food on seaside restaurants. Visit Dolmabache Palace on sea side right on Bosphorus. Have doner kebaps. Visit Taksim square and the shopping street. Istanbul has plenty to offer.
Cairo would be same for you like Dubai desert.....unless you visit Alexandria which is much greener and good for the beach only.
I would vote 99 times for Istanbul out of 100.