I think UMDNJ is a much better school than NYU because of small class size (90) and faculty to student ratio. They don't have to compete for clinic chairs. Besides the professors are super caring and nice. The only problem is location-- it sucks. Besides, the facilities are pretty comparable. UMDNJ is much cheaper than NYU.
On the other hand, NYU is freaking expensive because of living costs in New York city. The vice dean sucks and the class size is 360. They have very few clinical requirements like 3 crowns while UMDNJ requires 21-25. Other clinic reqs are also very minimal at NYU, which means you won't learn a hell lot in NYU. But at UMDNJ you will learn a lot.
Speciality rate for UMDNJ is around 23% which is comparable with NYU. But NYU emphasize heavily on research, which UMDNJ does not. So, if you like to do research, which many dental students would not opt for, go for NYU. otherwise, UMDNJ.
Finally, I think UMDNJ is a much nicer school in terms of creating a community with your classmate. They share notes of facebook and people are really nice. But from NYU, I saw a different vibe.