I have to go with Qbook being harder, at least for me. So without calling anything harder or easier, this is what I think : qbook tests a lot of specifics
it has also, in several q's tested specifics not mentioned in the kaplan books. For me, specific enzymes, cell markers, etc, are harder than some of the stuff in qbank. I havent done the qbook path yet, but in general I do better on qbank, and when not better, I am more often sure of my answers.