Yeah I'm doing it now.
Kaplan has quite a few zebra questions and quite a few "gotcha" questions asked from different perspectives.
In a way, the kaplan questions are "harder" but mainly because of good old "tricks and traps." Some of the concepts in there have helped me surviving pimping
(Ex. I was doing a GI question and the answer was something called Mirizzi Syndrome. At the time I thought: "When would I ever have to know this?"
A few days later, my general surgeon pimps us on biliary disease and describes Mirizzi syndrome. Imagine the surprise on his face when I answered his question in no more than a few seconds)
Personally this was my study schedule:
USMLERx first (easiest questions, gets your foot in the door, esepcialyl with the high high yields; but not representative of the real test)
Kaplan QBank next (learn some of the zebras and pitfalls in test taking)
Pretest questions (I know there are a lot of imaging, actual procedures, and frustrating questions in the sense that you will often scream "where was this taught?" but I find the extra knowledge quite useful... more so for the wards than board testing though)
UWorld at the end. save the good stuff for last.