According to previous rounds, Madrid (with 8,08) and Tokyo (8,02) have more chances (Istanbul is in 6,98), but you never know, Rio had one of the lowest marks and they won just because it was gonna be the first South American city to host the Olympics.
Advantages
Istanbul: first time ever in Turkey / country growin economically
Madrid: they tried it so hard many times, third time in a row / 80 % of the infraestructures are already done
Tokyo: the continent thing / more hotels seats
Disadvantages
Istanbul: repression over protests have thrown a bad image on Turkey / least developed candidacy
Madrid: financial situation throw bad image on Spain, despite there is no need of big investments here
Tokyo: already hosted Olympics / less experienced in these events in the last years
I really hope Madrid gets it after three bids, cause that would mean WORK!!!