I had an Undulated once. One day he must have woke up on the wrong side of the bed because he almost wiped out my entire tank. He cost me alittle over $100 in one night! The only survivor was a stupid blue damsel. Why is it the cheap fish always are the last to go?
As far as aggression goes inch for inch I'd say the Undy is the most aggressive fish for saltwater. The Queen, Clown, and Titan get alot bigger though.
Have you guys seen this guys site? Talk about some aggression.
http://community.webshots.com/user/espo72
There is a pic in there of his Bumblebee Grouper eating his Tessalata eel!