2-piece slotted rotor.

import111

differences:
1. A 2 piece rotor usually uses an aluminum center (hat) which transfers less heat to the wheel, and there for, wheel bearings and other parts.

2. Because of that aluminum hat listed above, 2 piece rotors weigh less, which lightens the car as a whole, lightens the front (which is good if the front of the car is the heavier part), and gives the brake pads less weight to clamp onto which in turn should make for shorter stopping distance (if the tires can manage).

3. From what I have seen in 2 piece rotors, the cooling veins are better designed to evacuate heat.