I don't know a single person without UWorld. I think that's basically a necessity.
As far as the self-assessments go, I bought them but haven't taken one yet. There are basically only two (or three) realistic options when it comes to self-assessments: NBMEs and UWorld Self-Assessments. I think the general consensus is that the UWSAs are not as accurate as NBMEs if you're using them as a diagnostic or to chart your progress. That said, the NBMEs suck nuts from the standpoint that they don't tell you the right answer even if you pay the extra money to review your questions. They just tell you what you got wrong. The one NBME I took was paid for by my school and they had bought the extended feedback version. I remember looking at my answers and going "This is simply not $10 worth of extra service (or whatever it is they charge)."
From what I understand, UWSAs give you the correct answers and explanations for them.
Like I said, I haven't taken one yet and I'm just going off my NBME experience and what I've seen people say. I think it probably depends on what you're looking for. If you're looking for maximum predictive accuracy at the expense of all other considerations, I think most people will tell you to take an NBME. If you're looking for a rough idea but would like your diagnostic to do double duty as extra Qbank questions, my guess is that the UWSAs are better.
I might take a UWSA in a week (if I don't decide to just do another NBME). If I do, I'll be sure to tell you what I think.
