the most common wear I've seen on rotors is in the middle (cupping) this is because there's more force applied by the pad to the center due to the caliper. Sintered metal pads will wear the center much faster if you let them wear down to almost nothing. If you watch them and replace when they start getting worn you can make rotors last much longer. A solid rotor will extend pad life if you run in muddy conditions, this is because there are no voids for grit to get into to cause excessive wear. If you don't run mud alot there's a danger of heat checking on solid rotors because they don't cool as fast as drilled or slotted. I run sintered pads on slotted rotors for mud, haven't have a problem yet, check your brake pins to see that they aren't worn, if they're worn the pads may not retract normally causing brake sticking that wears pads faster. After every ride take your pads loose and clean them, and grease the pins. Good maintenance pays off.