As I've posted before, Kaplan's QBank has a couple of strong areas that I've noticed- 1) What would Jesus Do type questions (these are pretty key I got a few of these on my exam and a few on each NBME... you really do need to practice these as the correct answers are never what any sane person would do. you need to learn what they're looking for). 2) Biostatistics - They have some pretty good biostats questions. In particular i remember questions regarding constructing one of those 2x2 tables given sensitivity and specificity... stuff you could probably figure out on your own but you don't want to see for the first time on the real exam.
For everything else I thought UWorld was far, far superior in quality. But those two areas stuck out. I would ask chip in with friends to get a month of qbank just to go through all of those questions or find a friend who has finished their qbank. The WWJD questions in particular were good in kaplan. UWorld had some great biostats questions but it had some gaps covered by kaplan and vice versa.