The dental decks are the only true "review" item out there for the NBDE I. So I would definitely suggest buying them and going through them. I also bought all of the released ASDA exams and went through all of them (from 1978 - 1996). Here's what I thought after the exam.
DENTAL ANATOMY: The decks and the old exams were a good review for dental anatomy. The cover most of the stuff on the exam (enough to probably pass), but they aren't necessarily everything. There was some question about the definition of fusion (or maybe gemination?) that wasn't covered on the decks.
ANATOMY: While going through the decks, I looked up in Netter's each card that had to do with Gross Anatomy. By doing this, I was able to review the relationship of the structures and innervations.
BIOCHEM/PHYSIO: I went through the decks and old exams, but I also reread a good chunk of my biochem notes. However, I thought this section was the hardest (and it was my lowest score), mainly because of the physio. I don't think our physio course was very good and it wasn't geared for the boards. In retrospect, I don't really know how I could have studied differently for this section.
MICRO/PATH: In addition to the decks and old exams, I would definitely recommend using First Aid for the USMLE and read the micro and path sections in that book. I read all the other sections in that book, but it was definitely best for micro/path. I say this only because my classmates who did only the decks/exams all thought this section was really hard. However, as I was taking the exam, there were at least 5 questions that recognized straight out of First Aid that I hadn't encountered on the decks. There was also a question about HIV proteins that I know I got right only because I remembered hearing it in class - it was definitely not covered on the decks.
The best way to be prepared for this exam is to study hard when taking the courses in dental school. This way, you'll have a good foundation when reviewing for the exam. For example, our school does a really thorough job preparing us for dental anatomy. So yes, a student from my class could have only done the decks and the old exams and scored a 90+ in dental anatomy, only because he/she had such a rigorous background in the subject.
If you feel weak in any of the other subjects, you could try picking up some review books for the USMLE (the med school boards). There are tons of USMLE review books for every subject (Anatomy, Physio, Biochem, Micro, Path). They would probably be a good review for the NBDE if you feel totally lost.
I can't comment on Kaplan because I didn't have time to take it and I don't know anyone in my class who took it either.
