In short, US immigrants will be more African and much less Hispanic 15 or 20 years for now.Hatton and Williamson (2011)
The linked article that appeared in the journal World Development cites that currently in the US 41% of immigrants are from Latin America and the Caribbean and 6% from sub-Saharan Africa. Countries with more children and lower economic growths rates in the past have seen higher rates of immigration. Since Latin America has lower birth rates and higher income growth than sub-Saharan Africa they predict that African immigration will increase faster. Their model predicts sub-Saharan African immigrants will make up 15% of US immigrants in 20 years, while Latin America/Caribbean will drop to 33%, the rest of the world will stay about the same.