There are 39 different districts in Istanbul but most of the hotels and historical places are in the city center. So most of the passengers have a destination in these areas. These districts are Şişli, Beyoğlü, Fatih and Beşiktaş. As tourists like to be close to historical places and tourism attractions, most airport transfer reservations are to these destinations. It is almost the same distance from these destinations to both airports but there are differences because of traffic. Sabiha airport Gokcen ( SAW ) is in the asian side of the city on the other side of the Bosphorus. 

Every weekday there are lots of people who want to pass from the Asian side to the European side in the morning because of their job and want to return in the afternoon. There are 4 main roads to pass from Bosphorus, 3 bridges and one tunnel. One bridge and the tunnel have high tolls so most citizens of Istanbul do not use them. The population of Istanbul is around 16 million, so you can imagine what will happen when the residents of the Asian side who have their work in the European side want to pass from just these two bridges.

So for the passengers that  their flights land in Sabiha Gokcen airport in the morning, it takes around one hour and half sometimes to reach their destinations on the European side. But maybe it won’t be so important as it is the arrival, the big problem will happen when somebody has a flight from Sabiha Gokcen airport in the evening. It can take up to 2 hours to reach the airport sometime and you need to leave your hotel 5 hours before your flight to have the guarantee to not miss the flight. In any case if you don’t have enough time you can ask your driver to use the Tunnel, especially when your hotel is in Fatih district, it can make it to reach the airport half an hour or more earlier.

There are no such problems when your flight is to Istanbul New Airport. Just if your flight is from Istanbul Airport in the morning and your hotel is on the Asian side like Kadikoy or Uskudar, in these cases also you need to leave your hotel 5 hours before your flight. Or sometimes there is lots of traffic when your hotel is in the SultanAhmet area, so you need to leave a little earlier than normal.