Auto-Attack can be define as: The ability to use an action automatically on a target based on a predetermined time interval.
The reason we need to define this is because people ask for it without fully understanding it or what they truely want. Auto-Attack is neither fast or slow by nature but rather the time delay given to them. Two examples of this are as follows.
World of Warcraft: Fast paced combat based on the use of abilities rather than standard attack with fast cooldowns (seconds).
Final Fantasy XI: Slow paced combat based on standard attacks rather than abilities with slow cooldowns (minutes).
Now the question is do you want a fast paced battle system that burns through enemies quickly commonly dubbed "Tank and Gank" or a slower approach using tactics and strategy?