I guess that depends on how you're driving them and what power sources are
available. Both of these systems can be driven by servo drives or more
basic variable-frequency drives (AC) or pulse-width modulating drives (DC).
The sophistication of the drive means more to you than the motor.

For precise position control go for AC servo, especially if you have
three-phase power available. Be warned that these are expensive and require
a bit of knowledge (and software) to set up. Look on EBay and you'll find
many makes and sizes of both drives and motors. They need to match in many
ways: power output, feedback device, cabling, etc.

For speed control only you can use either an AC motor with a VFD or a
brushless DC and a PWM drive. For overall speed control and power-to-weight
ratio I'd go with the DC.

What's the application?

Regards,

Damian

"elitkh" wrote in message
oups.com...
what is the benefit of each system?
thank you
eli