Depends on the application. For smaller servomotors, Beckhoff has slice modules that drives them directly w/ servo-feedback, which seems the easiest PLC interface. Their larger drives are stand-alone boxes, which used to use Sercos III so perhaps that still exists underneath. Beckhoff's larger servo-motors now have 1-cable connection. It seems primitive to require multiple cables per motor today, but either way insure the connectors aren't expensive and hard to source.
There are many types of motors used in automation (stepper, DC servo, AC) and many control modes (speed, position, torque). For a home CNC app, I have 24 VDC motors from Dunkermotoren with integral speed controller, so the PLC need only send a +/-10 V speed setpoint. The controller existed as a separate board in their earlier motors. Integration is usually nice, since cables and connectors add much installation and support costs. Depends on your maintenance approach. Separate boxes can make trouble-shooting easier and repairs cheaper, if you will run problems to the source. For fast repair, replace-it-all is best, and an integrated system makes that easier, if you can afford to stock spares.