Before you go replacing parts, how did you go about trying to eliminate the rubbing? First, have you confirmed that the wheels are seated firmly in the dropouts? Have you already been through the basic set up procedure for aligning the caliper to the rotor? Have you checked that the rotors are true? Have you checked that the brake cable isn't binding anywhere and that the caliper arm is fully returning after releasing the brake lever?

You get more precise alignment, better feel, and easier adjustment with better disc brakes, but cheap disc brakes can be made to work with a bit of effort. And on the plus side, once set up, you'll basically never have to touch those adjustments again.