Uneven Disc Brake performance
You say the rotors are relatively new. Have they been bedded in properly? The usual procedure is to get up to about 30km/h, brake hard until you almost stop, and repeat. You should feel the braking power picking up each time you do so.

The bedding in process transfers some pad material to the rotors - this is what the pads grab, rather than the actual steel surface. It should be done any time rotors or pad compounds are changed.