Servo systems are closed loop positioning system, allowing great control over velocity, torque and position. The drivers will need to be fine-tuned per use-case. The DMM series servos support autotuning and hence can calculate the PID parameters. Hybrid stepper motors and a complementary driver provide closed loop control, but lack speed and instant torque as with servo systems. Stepper motors provide stepwise motion from one equilibrium position to the next and are not equipped with feedback. A rotary encoder can provide feedback to the control system.
Which to choose ?
The advantages over a stepper solution is that they are often less complex to install and are therefore more cost-effective. If higher performance or more accurate positioning is required then a hybrid stepper or servo system is recommended.