Disc brake pad and rotor compatibility
I have to say I never consider which pads I'll be using with rotors when I buy either. I buy organic for best stopping power and metallic for longest life (kevlar somewhere in the middle). 

For mountain biking, the weather and type of mud/grit you're riding on is a FAR greater killer of pads than a rotor; you can easily get through a new set of pads in a few hours in sandy and wet conditions.