Slotting in general creates less of a stress factor than a drilled hole. Slotting is useful to scrape down the pad face, and keep it clean in applications where that may be necessary. Racing, and Rally etc type applications are the most notable examples.
Run, don't walk, from any drilled rotor that hasn't had the edges properly radiused. Radiusing the edges of the holes will decrease the stress concentration, but nowhere near eliminate it. So basically, its a little better, but not enough to make it worthwhile. Further, cooling benefits of drilled holes are minimal, and even possibly negative in a rotor not very specifically designed to make use of them. Very few rotors designed like that exist. Further, even when designed to use them, the benefit is minimal over a properly vented plain or slotted rotor. Plus, no matter what you do, a drilled rotor will still crack sooner than a similar plain faced rotor.
