Rocks won't get in there, just like they don't now, that what the rock guard if for.
Now drilled, you will FEEL the drill holes when braking, ask me how I know.
Go with slotted, that helps get water out during heavy rains.
Even better get Angled Vaned rotors. Those are side specific, the design is curved into the air, grabbing it and channeling it inward towards the center providing more cooling than the straight vaned jobs. The longer angled vanes also add to the cooling compared to straight. No more warping on long down hills or towing efforts. Luck.