DC v AC

I'm by no means an expert on the topic, but here's how I understand it. Pure DC doesn't have power fluctuations as AC does, motors are more efficient, quieter and easier to maintain a stable speed. No matter how much AC conditioning and power cord upgrading one does, the AC motor is still an AC motor and can hum. AC motors can be more powerful, but not much power is needed to drive a platter, which is why you see a few AC-driven decks use some sort of current-reducing circuit to reduce power after the platter is up to speed. (Less current equals less noise.)

Don't know how technically correct this information is, but I think it's a start to answering your question.

The cogging factor Doug points out is one of the larger differences between AC and DC motors. Synchronous AC motors reduce cogging, but not as effective as DC in this area.

I chose to go with the OL DC motor kit because, for $500, it solved problems that would take at least $2000 to solve with an AC motor. (conditioning, motor controller, power cords, etc.)

Jim