My philosophy for Kaplan is, it's not incredibly accurate. The reason is, a lot of the questions are quite tough (for PS), and so you end up guessing on a good deal, so if you're lucky, you'll do well. VR is another story: too dense passages, and questions that require you to go back to the passage far too much thus killing more time, ending up not finishing, guessing on some questions = overall, just bad VR.
By some miracle, my Kaplan score still is in range to AAMC (got 30's, 31's, 32's) for both tests.
I'm going with AAMC, just because my grade is never fully a surprise for AAMC. I can always guess pretty well right before I get my score.
Kaplan, totally can't guess.