I did 7, 11, 12, and 13 along with both UWs; if i had to pick one it would definitely be NBME 13. UWSA 2 had a pretty ridiculously generous curve and i felt the questions were much different than UW 1 and the NBME exams. On the other hand, i felt NBME 13 was a good test. I have not taken Step 1 yet, but it seems the later NBMEs are most representative of the real exam.