Slotted rotors are better (long term reliability) when the metal is drilled it is prone to fatigue cracking. The absolute best would be cast ceramic rotors (read porsche 911 GT2) since the holes are cast into the material they are less likely to crack. Slotted rotors will not crack and shed brake dust and heat almost as well as slotted. Drilled and vented do perform the best but have to be inspected more often. So get out your micrometer.