I would say the Murray Cod, They get reaal big, and make a great aquarium specimen, If you have enough space and money. 
EvilMonkey666 said:I say largemouth...when I caught mine at 4in..he was a bastard...what a miniature fight!
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I strongley agree with CM.CentralMayhem said:large full grown 20+" undulated or titan trigger would demolish a snakehead or any of your other fish. their skin is impenetrable with knifes, their mouths although small can break throgh rock or bone with absolute ease. a full grown undulated trigger would probably be the meanest fish if put in the position of being able to scrap it out in a home aquarium. never being possible to fight Channa spp. with any oceanic creature in freshwater, i would put them AT or CLOSE to the top of the list of meanest fish. all fish are not created equal though.