I'm doing as many questions as I can get my hands on. UWorld is my go-to source, however, and just because you've done it once doesn't mean you can't do it again.
Whether or not you remember the answer to a question is irrelevant. What matters is do you understand why the answer is what it is, and why the wrong answers are wrong? I have learned more from my second pass through World than I did from my first pass.
So yeah, Kaplan is fine. But just because you've done all the questions in World doesn't mean it doesn't have any use to you anymore.