AC vs. DC Motors

In my opinion, the main difference: AC is fixed speed, DC is not:
"Most AC motors run at a fixed speed determined by the AC line frequency. In the US, this is 60 hertz. Current determines a DC motor's speed, so most applications requiring a variable-speed motor use the DC variety."

sources:
http://www.ehow.com/facts_6324935_difference-between-ac-dc-motor.html