[RyanCahoon]

I'd be hesitant to use a stepper motor (assuming you mean without any additional position feedback); they're can be good for controlling velocity and can control position in low-load scenarios, but if the motor is prevented from turning (pushed against a wall or something), your program won't have any way to know the motor is not in fact turning. Also, steppers require special controller circuitry, so you would have to figure out how to interface with that.

In regards to a servo, there's no reason why you couldn't use one, as long as you found one with enough torque, as has been said. Note, however, that a servo is just a motor and potentiometer anyway, the only difference is the sensor and control circuitry are contained in the motor shell (at least for most of the hobby servos, there are ones with external controllers as well), so by attaching a potentiometer to a motor, you are effectively creating a large servo. The difference being that you have to code the control algorithm yourself, which could be a pro (ability to tweak PID parameters) or con (have to go through the work of tuning the system, perhaps reduced response time), depending on your requirements.

--Ryan