Steve Sailer blogs about the book Breeding Between the Lines: Why Interracial People are Healthier and More Attractive by Alon Ziv. The title of the book presumably explains what the book is about.
Steve writes "I'm not fully convinced by the evidence for much additional hybrid vigor from marrying intercontinentally." I, however, am completely convinced that Jews would be better off marrying non-Jews, because Jews are especially inbred and have a lot of bad recessive genes in their gene pool.
I also believe that white Americans are, on average, better looking than white Europeans, because Americans are more likely to be a mix of genes from different areas of Europe. I can't help but notice how ugly people look in some of the more inbred areas of Europe, such as the Balkan countries.
But is a white American better off marrying a black, Asian, or Latin-American in order to have genetically better children? That's a very different question.