I took 9 Kaplan Full lengths and 7 AAMC tests.
Average Kaplan tests: 32.5 --> Kaplan full lengths are more difficult however they are curved accordingly. The problem with it is that there is more "room" at the high end of the curve.
Average AAMC tests: 31.5 --> Much easier than the real MCAT, but the curve is extremely harsh.
Actual MCAT score: 32.
The difficulty of the real thing was in between the AAMC and Kaplan full lengths. Frankly they may be nearer to Kaplan in difficulty, but once again the real MCAT has experimental questions and is curved according to how people do.
So I recommend taking the Kaplan FL's except for 10 and 11. Supplement it with AAMC tests.