It depends upon what your priorities are: noise, efficiency, simplicity, cost?
If I wanted to keep the noise down, keep the efficiency up, and control speed, I'd be modulating a DC supply with a 16-20KHz PWM signal. An electrically isolated mount or some other means to limit current flowing through the bearings might be needed though. Better efficiency implies more torque before you stall or overheat.
If I needed simplicity, low cost, and didn't need the speed controlled, I run it with a triac or a relay connected to an AC supply. A relay won't last forever with a motor load but a triac needs a high dV/dt and a snubber circuit to switch inductive loads.
Any other combination of noise, efficiency, simplicity, and cost would depend on the application.