As others have said, stick with Uworld unless you have a compelling reason to venture into kaplan qbank territory. For example, I did my first run of Uworld alongside my 3rd year clerkships, starting with surgery and ending with medicine. As expected, Medicine is the bulk of Uworld, and since I took step 2ck 4 weeks after my medicine shelf, I felt like a majority of the qbank would still be in my memory. So, I did the kaplan qbank specifically to buffer my memory of the uworld qbank. Once I finished kaplan, I then did a second run of uworld prior to taking step 2ck.
I scored >250, but I most definitely do not attribute this to kaplan, uworld was right on the money for my test.