I'm no expert on NJ dope, I just know what I have read on this forum. I started my "dope career" in 2006, and what I was getting was coming from Brooklyn.
From what I have read, NJ (Newark and Paterson to be specific) used to be a lot more consistent back then, and the prices were, and still are lower than NYC prices. So it would make sense for some people to make the trip from NYC to NJ, especially if copping off the streets.
Fast-forward to today, and the general consensus seems to be that NJ has fallen off in quantity and consistency, with the exception of Camden which has consistently high quality fat bags, but you are paying more for them.
Edit: I think that Altek can co-sign to what I wrote, and probably knows more about it than me.
NYC is still consistent with its fat bags of good quality dope, with stamps staying the same for a long time. Newark and Paterson stamps are a gamble, with knock-offs, and changes in quality all the time, but for a lot lower price.