Magnum Force or Black hole have the most powerful brakes. They hurt. Magum Force hurst because you stop so quickly, you are thrown forward and then back, and you hit your head on the seat. Black Hole hurts because of what Gouldy said, with the 1 behind the other seating, it hurts if you are at the front.
Oblivion also has to get a mention. Ive sat there for ages, but i dont mind it that much, its a good photo oppotunity.