As pstm91says, traffic in Istanbul is horrendous most of the time. It might not be too bad very early in the morning, but it would still take a minimum 45 mins from Sirkeci. I normally try and stay in hotel brands I know, just because you know what to expect. If you want to spend some time in the hotel the day before you leave then the Raddison Park Inn is 15 mins from the airport, has a swimming pool, restaurant etc. Alternatively, if you just wanted to turn up, sleep and then get up for your flight the Yotelair hotel would work.