Where I'm from everyone takes Kaplan, they almost have a monopoly here. However, a friend and I took TPR for some reason. Out of the 10+ people I know who took Kaplan, I think the highest anyone scored was a 30 or 31, most in the high 20's. My friend and I both got 35's, which neither of us expected to get.
I think Kaplan's practice tests are too easy. TPR's tests, however, are too hard. So I recommend using the AAMC practice tests no matter which course you choose. I think TPR's workbook was most helpful. It was easy to carry around and practice anywhere, rather than having to be at a computer (i.e. Kaplan).