Microstepping will usually give a little less torque. But the motors run smoother. half step would maybe give you slightly more torque (wer'e talking maybe 5-10%), but the motors may not run as smoothly. It's easier to miss steps with a rougher running motor, though. Usually you'll be better off with microstepping. But every situation is different, and you might be better off with half step. Trial and error is the only way to know for sure.