Neither, actually. The cross drilled are prone to cracking if the holes are drilled after casting. If the holes are cast into the rotor, they are a little stronger, but for street driven they really do nothing. They look cool, but that's about it. As far as slotted, they do dissipate heat, but think of each slot as a little knife, slicing away at your pad. What you want is a vented rotor, they will give you longevity and heat dissipation. Your best bet for street driven braking performance is a larger diameter rotor, and you only need the front, cause the rear won't do much but cost you money.