This is related to my previous question: How many survivors would grow on earth years after a worldwide nuclear holocaust?
In an earth with roughly a billion modern day survivors, and 20 million former USA citizens are trying to survive and organize themselves after nuclear holocaust, which areas (specifically the area in the former USA) would have the greatest success during the 10 year nuclear winter (soon turning into cities)? For example, those living in the center of a large area of good farmland, for instance, will always have an advantage over those who are alive in the middle of the Appalachian or Rocky Mountains, simply because they've got a food advantage.
As such, to be considered successful, the areas need to have a relatively staple production (or import) of food in order to maintain and grow the population. Also, areas more likely to recover and/or to turn into cities (and therefore with higher population) will be considered more successful. In case it is not possible, consider the areas with the lowest decrease in population and highest sustenancy instead (even if it is insufficient).
This is under the assumption that large population centers like Chicago, New York, military installations, etc, were specifically targeted by nukes. By large, I mean greater than 500k population.
For reference, the nuclear strikes started at January 1 2020, and targeted specific countries such as USA, Canada, Russia, China, UK, France, India, Pakistan, Italy, Iran, Korea, Israel, Saudi Arabia.