I did med school at RWJ Camden, an intern year at UMDNJ, (a 2-3 program in NYC), and came back as an attending at BI, so I know them all pretty well.
BI is pretty similar to UMDNJ and Cooper. The acuity is high, plenty of procedures, great group of residents to work with, always plenty to do. In the last 3 months I've been on I've had a perimortem c-section, floated about 5 pacemakers, a bunch of chest tubes from walk in stabbings and GSWs, some nice difficult airways, etc. Residents do everything, we bail them out if we have to, which is pretty rare. The ultrasound program is well developed and we have the busiest peds ED in the state. I think the residents are really happy overall - it's a resident run department and they take pride in it. Trauma is at UMDNJ, another month at Jersey City Medical Center for trauma, and most of the other rotations are on site. The graduating residents do really well with job placement and fellowships.
I think Cooper has a great program as well and there is a lot of potential at UMDNJ. Morristown residents love their program; it's a different patient popluation, and some people will prefer that to working in the inner city. I'm friends with attendings at all of these places and they all like their jobs.
I don't think you can go wrong with any of the programs in NJ. Best of luck with the process.