This isn't the 80s any more - Harlem and and the South Bronx aren't the war zones they used to be.
As a clean cut white guy, long since out of his 20's - I would never be mistaken for a gang banger. So on that level, I'm not worried at all about either place. Doesn't mean I would exactly be comfortable, but moreso because I dislike being in unfamiliar neighborhoods late at night and don't want to look out of place and therefore inviting of a random robbery/mugging.
Regarding the OP: I'd have to choose Compton, since I know how to get home from the Bronx or Harlem; and LA is a long long way from home.
If I were allowed to freely pick a city? Camden, NJ. The FBI seems to think that it's not the "#1" most dangerous for last year, statistically - But know that they laid off 50% of the police and fire departments early this year.