Moscow, London, Paris/Marseille, Rio de Janeiro/Sao Paulo, Tokyo or Hong Kong.
Screw Dubai. Fake boring city with no crime. Hell, women go to jail for having casual sex there.
If it has to be the US again, Washington/Baltimore could be a good idea (You have "The Wire" angle with Baltimore and a port, plus the whole government angle with Washington though it could touch certain aspects which might be risky i.e. terrorism - just imagine a Trevor character rampaging around the White House - could upset some people). I wouldn't mind Chicago, Detroit or Boston. No more Vice City. It's time for change.