Which neighborhood is home to a significant number of Puerto Ricans and Dominicans today?

The Lower East Side is recognized as a historical and contemporary hub for Puerto Rican and Dominican communities. This neighborhood has undergone significant demographic changes over the years, but it has remained a vital area for these cultural groups, especially due to its rich immigrant history. The presence of cultural organizations, businesses, and community events underscores the influence of Puerto Rican and Dominican heritage in this part of New York City.

In contrast, while Harlem has a deep-rooted African-American heritage and has seen some Caribbean migration, it is not predominantly known for Puerto Rican and Dominican populations today. Williamsburg has become more diverse with various ethnic groups but is primarily recognized for its artistic community and gentrification processes. The Financial District, being the economic heart of NYC, does not have a significant residential population, especially not one that represents the Puerto Rican and Dominican communities prominently.

Thus, the Lower East Side stands out as the correct answer due to its meaningful and ongoing connection to these cultural identities.