Cross Drilled Rotors are basically rotors that have been cross drilled to allow the heat that builds up between the brake pad and rotor to escape through the drilled holes. Drilled rotors look great and are often considered an upgrade over OEM blank rotors.
Slotted rotors improve reliability. Slots help pull brake dust away from the pads, allowing more of the pad’s surface area to come in contact with the rotor, which translates to better grips and better stops. Basically, you can stop your vehicle faster with the same effort.