If you're primarily trying to date BW, then you can pretty much eat in any city with a major black population.
If you're trying to date interracial, then you should avoid the northeast. Honestly the new south (VA, NC, GA, FL, TX) are probably some of the best places if you're tryna to date pawgs. West coast if you're into mexican and asian chicks and also white women.
So to answer your questions.
1. The worst place if you don't want to be restricted by your race is NYC. If you want black women and latinas it's great. But outside of that, it'll be far more difficult than most other places in the country. Blame the aggressive ass new york nikkas for that.
2. The worst place if you want to date only BW, would probably be the midwest, or really any state that has a low black pop.