I plan to stay here on points from 5/6 - 5/8, so it looks like I might provide the first feedback on EDITION Istanbul.
The location is in the business district, conveniently situated near the Levent Metro. The Ritz is more well-suited to tourist/nightlife, as it is closer to Sultanhamet/Taksim.
I stayed in the Ritz in 2006 and the views from the rooms were stunning.