Go with Kaplan. I have very bad study habits and I was able to pass MCAT above national average just following their prep course. Same thing now with Step1, I have bad retention, but I'm in the middle of Kaplan prep course and my score improved from 175 (pre-dedicated) to current 212. I'm half way through, 2 more weeks to go. I'm hoping to get about 225-230. They give you only what you need to know - which is good and bad. Good because you can improve score quickly. Bad because you'll not hit really high scores like 260 using only Kaplan prep. However, for most of us who needs improvement it's that portion of scale from 180 to 240 that matters most.
Our school puts those who need help stat (due to time constraints) on Kaplan Prep course. They are basically betting their money on it (they don't want a 2nd year student to fail - both for monetary and statistics/reputation purposes). If there were some other course as good as Kaplan - they would't have hesitated to offer that.
Just my opinion man.