I'd say there's no best predictor. I scored on the practice tests anywhere from 26 to 34. I know its impossible but just take the tests look at what you did wrong and forget about the scores they give.
No joke!! On AAMC II I got a 36, but on AAMC III which I just took today, I got a 31. It's so uplifting at times and at other times, it's the pits. Just keep hope and keep on taking practice tests.