Well, honestly, unless you are racing, or are an extremely agressive driver, I do not recommend using aftermarket rotors.
The reason why is that you will not use the features of the rotors.
Normally, you have 3 types, crossdrilled, slotted, and a combination of the 2.
Slots and crossdrilling do almost the same thing, they permit outgassing. This means that as the brakes pads get hot, they emit gases. If the gases are not vented off, they get stuck in between the rotor and the pads, and cause the anomoly known as brake fade.
Crossdrilled, usually is used when you are looking to reduce weight, and vent the gases of the brake pads when they heat up. The downside, is that under severe use, they sometimes will fracture around the drill points.
Slotted are usually just for outgassing, and do not reduce weight. This is usually the best for street driven vehicles, that are driven agressively.
Slotted and crossdrilled do both and are usually more expensive.
I hope this helps, and welcome to the CAC, c4c5
Thank you very much for you detialed reply. I need to replace my front rotors and the information you provided will assit me greatly in my decisions. Thank you very much for you time and very informative advice.