I used both the RXPrep math q's as well as the SDN 120 math q's. However, I knew going into the naplex that math was my weak spot. My opinion is that the naplex cover a extremely broad range of subjects, but you are guaranteed to get math. So those questions you should have down pat in order to give yourself the best shot possible.
Other than math, I would review your weak spots. If you are good at DM, HTN, cardio - then focus on other things. I recommend making a pass through HIV and oncology. Topics that you may be less familiar with and the naplex may target. I definitely got questions in both those areas.