servos and stepper motors are two completely different things,
servos have 3 wires...
steppers have 4-6 wires...
a servo is a basically just a dc motor with a gearbox, feedback and controller circuit built in.
a stepper is a motor with 2/4 electromagnets built in and it turns them on one after the other spinning the magnet in the middle.
steppers are much more accurate than servos but are much more expensive,
look up info for both and decide which you want.
if you need speed i would say go for dc motors with controllers...