The nice thing about DC motors is that they can provide torque over a range of RPM. Also, brushless motors reduce the friction.
I believe that DC motors (with proper motor controllers) are more efficient when the load and/or velocity requirements change. For constant load and constant velocity, three-phase motors simply rule.
Tesla was a really wierd guy, but unbelievably insightful. AC is faaaar more efficient at transferring energy to disparate devices over long distances, especially with the primitive technology available at the time (they didn't exactly have good DC to DC voltage changing devices at the time).
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