Some Ideas
The Immigration topic most captured my interest. I want to see how Berlin as a whole functions not despite but through its diversity. I am also arrested by the idea of a collective identity: so it would be very interesting to see how all these influences form the confluence. Much identity is found through the future of the city, namely the youth. Perhaps comparing views of different Berlin youth, from Turkish to Eastern Jewish to German Jewish to German (and having many generations living in Berlin). Also the relation to class and financial differences and how that affects Berlin immigrants or youth, as opposed to it here. An focused interest: health care (in immigrant populations or otherwise).
The roots of differences, confusion, or division might be specific to Berlin, and there might be significant parallels between Berlin and other areas such as Seattle. The trick will be to see the similarities but also identify how Berlin is unique in its issues, in the attitudes of its peoples, and in the peoples' methods of handling the issues.
The short version is: my top three are immigration, youth culture, and health care.