As someone who struggled with all the step exams and the boards and really had to pick it up from a marginal step 1, I want to just add that honestly the resources that are good for each person completely differs.
I did UW x 2 but I found UW to be a bit almost too tricky and sure although the stems and answer choices were devious, I didn't find them to be that useful because I felt it was almost unnecessarily too convoluted. MKSAP felt much more natural to me when I started doing it, and although it seems kind of "basic," it does cover all of the topics you need (skip all of the MKSAP updates though and any question that has a link to an article -- that is not meant for actual board prep).
If I learned everything from all of my steps and ABIM, it is that for the people who failed and are struggling to pass, blind repetition of answer banks are NOT going to help. There is usually something fundamentally wrong with the way that you are consolidating knowledge or recognizing testing objectives from the questions. You can do UW and MKSAP to death and all you're going to end up is memorizing the answer choices, and that is just going to lull you into a false sense of security and eventually delude you into thinking you will pass, but just to fail again when you walk into the testing room because the actual questions will NOT be the ones you have already memorized from UW or MKSAP. I strongly believe that with anyone who has failed or come close to failing, it is necessarily to sit down 1-on-1 with live human being (heck, take a prep course if you need) and diagnose what exactly led to the fail (is it lack of knowledge, poor test taking skills, poor comprehension/reading ability, or anxiety?). Even sitting down with someone who did well (coresident or co-worker) and going over a couple of questions blind and "thinking out loud" why each answer choice is either correct or incorrect helps tremendously in picking a target to focus on for the next time around as hopefully your friend can help diagnose what is wrong. I bit the bullet and did this between Step 1 and CK and improved significantly. The hardest part is being honest with yourself and forcing yourself to change your ways and get out of the rut you're stuck in.
The boards are graded on a strict percentage (not curved), so there is a way to tackle this thing. If you made it through med school and residency, you should pass eventually. However, for the love of Osler, blind repetition of qbanks or blind reading of MKSAP is not going to help you. Full stop. Period.
Also, if UW works, go for that. If you like MKSAP, good for you. Sure, everyone has an opinion, and here's mine.