The statement that BEST expresses a comparison between ethnic enclaves and instances of segregation in the United States is:
Ethnic enclaves develop out of voluntary chain migration, while segregation is forced legal segregation based on race.
This statement captures the fundamental difference between the two concepts: ethnic enclaves arise from voluntary choices made by immigrants to live near others from their home country for cultural solidarity and support, whereas segregation historically involved legal and systemic measures enforced by the government to separate people based on race, often against their will.