At NJMS, you get exposed to clinical stuff as early as the beginning of first year. You learn patient interviewing, basic physical exam all in first year, and you can get involved in the student-run family health care clinic from the get-go. Because NJMS is situated in Newark, a city with a significant population at or below the poverty line, you will get to see a lot of sick and complicated patients at University Hospital, and because it's near a major airport, you may even see some wild diseases you may not otherwise see elsewhere. It's also associated with the East Orange VA and the lush Hackensack Hospital.
The big thing everyone seems to talk about when comparing NJMS vs RWJ is location: Newark vs New Brunswick, respectively. Newark is rougher city overall, and New Brunswick has more of a college town kind of feel. But I believe NJMS has better clinical training overall because you are exposed to so many complicated patients.
I can't say much about RWJ. Hopefully an RWJ student/grad chimes in.