Odd answers, but on the street food side of things, my foremost favorite location was Ghana (primarily Kumasi and Accra), and Nigerian cities (many I've hit). I really like West African food and it's as cheap as it comes on the street, though one has to be willing to be slightly adventerous. I wouldn't be shocked to see West African cuisine begin to take off in the West in the next few decades woth some adjustments for our palates (less offal, more tamed spice levels, etc.).
In general, I love NYC's diversity as cliche as it is. Tokyo however, wins my overall favorite by a significant margin.