Dont mean to be a downer but this poll should be moved to 'The Aquarium' since it doesnt deal with aggressive aquarium fish.
But my vote is for the great white.
WHAT!!?? Sharks aren't aggressive Fish - since when.
Trust me - any one whos had a pet Horn, Epaulette, or Bamboo shark hunt down & eat their cleaner shrimp can tell you differently. Anyone that had their pet Coral catshark attack and kill other small fish that are tankmates can tell you differently. Anyone that seen a young wobbie attack a Puffer fish can tell differently. Or had a Bonnethead or Blacktip reef kept with crabs,stingrays or fish can tell you differently. Or what about the 100 or so people at bitten by sharks every year.
Sharks can very aggressive and very dangerous.
It's also of note that virtually every species listed on this poll have been kept in a Public Aquarium (at least for a brief period) at some point in the past 5 years - except the megamouth & the goblin sharks.