It used to be that drilled rotors were the only thing available and are highly regarded for their racing look. As you can imagine, drilling a lot of holes in a rotor creates a lot of stress ridges. While I have no experience with them on Hondas, Porsche racers have been known to have drilled rotors crack from fatigue. The holes are also supposed to make the rotor lighter and cool better. I have heard no evidence supporting this.

The groved rotors have the benefit of giving gases an escape route without significantly affecting the structural integrity of the rotor. In theory, they also give the pad and edge which to bite when the brakes are applied. Everyone that I know who races Porsches uses the slotted rotors. I have the drilled rotors because they match the period look of my street car. In other words, do you want to look cool, or reliably stop fast?

Rich