Of those three, I'd say Newark has had the strongest recovery -- which isn't saying much. Anything that close to New York is gonna attract folks when land gets cheap enough.
Camden, on the other hand, offers only proximity to Philadelphia -- a city that is itself in decline.
13 years ago, I lived in Cherry Hill for a few months for a job, and I did a lot of driving around on the weekends. Sometimes into Philadelphia to see the historical sites and the museum, and sometimes just around, since this was an area of the country I knew nothing about. Once, I made a wrong turn and ended up in Camden.
It was unlike anything I had ever seen. Every city has pockets of blight, but this was block upon block upon block without a single house that looked occupied or a single business that looked open. It was downright post-apocalyptic. My right foot was ready to punch the gas pedal and get the hell out of dodge, running every red light along the way, if it came to that.
In the more-populated areas, i noticed that people stepped back off the curb a little,as if they were hanging back and letting me pass. Gang-bangers on the corner not only didn't hassle me, but they seemed to be avoiding eye contact. These folks were scared of me?
Gradually, it dawned. My employer had rented me a Lincoln Town Car. Any 20-something kid with a ponytail and the b---s to drive through Camden in a brand new Town Car had to be with the Mob. Rutgers students were too smart to go into that part of town.
Detroit got a double-whammy. In the years when it might have recovered from the riots, the US auto industry, the vast majority of its job base, started a decline that hasn't stopped in the last three and a half decades. So now I could buy a well-built house in decent shape in Detroit for next to nothing, but once I'm there, what do I do? Where do I work, and where do I shop? It lacks the economic ecosystem for a place where people want to live.
Not to be contradictory here, but people used to say Newark “got that way” from being close to New York, especially after the transportation improved. Why go to the Mosque Theatre when you could hop on the 118 and go to Carnegie Hall? Ditto for the planetarium and everything else.