Disc bakes rock but most rotors are too large. Go with the smallest rotor you can find for better modulation. I use custom machined 2.5" rotors and adapters but you might have to settle for 4" as the bike companies basically only make really big rotors since they appeal to the "bigger is better" wannabe downhill crowd.

Big rotors suck though because they're too grabby for basically every application. I never need big rotors for the mountain biking I do, which mainly consists of riding as fast as I can along the edge of the local multi use path and bunny hopping dogs and children.