I did UWorld last year during MCAT prep and I'd preface my answer to how you'd be utilizing these resources. I'd say in general, practice questions are designed to help test content knowledge whereas FL are better for simulating the real thing so you know exactly what to expect. That sounds like a "duh" thing to note, however, if you're specifically looking at purchasing one of these just to bang out practice questions, definitely go with UWorld. If you're a couple weeks out from your MCAT and you've already done the bulk of your review, go with NextStep. I agree with the above poster about UWorld's explanations. They are absolutely second-to-none. I actually ended up ditching the majority of my textbook review once starting the questions bc they cover everything you need to know and explain why and how answers are incorrect, not just that they are wrong. Best of luck.