My personal favorites go to:

1) Goliath African Tiger fish

2) Yellow Tail Barracuda

3) Payara
And yes, I had to add a face for some odd reason
4) And of course the Arowana

1) payara.
2) great white shark
3) arowana

Holy Crap those are ugly fish!!!! Payara are those the same as a Saber tooth tetra??
My favorite Predators would be the following
1) SnakeHeads
2) Bull sharks also Known as Zambezi Sharks
3) Nile Crocodile

Bettas! Look at that face



Ferocious, right?

I like a nice group of black diamond piranha, although I know they dont like to be in groups like red bellies... but they look sooo cool as juvies all together in a tank.

My favorite is my Snapper!!!!

a childhood fav

turtles with fish ftw

No it's not an Alligator Snapper it's a color morph of a Common Snapper. If you want them to live with fish keep them well fed and the fish must be big and dispenable.

im sure a giant tank helps too..... one that the waste the turtle creates wont kill your fish... like in a 55gal, or 30gal... that would be crazy.

He lives in a 4' 120gallon with 2 Albino Oscars and 2 Syno. Eurpterus. There are 2 cascade 1500s for filtration and it gets a 50% water change once a week.

Arowana and Piranhas

My personal favorite.

http://www.youtube.com/watch?v=sdJRb7lVoGc

Arowanas, flowerhorns, bettas.... and I'm sure Lipochromis sp. "Matumbi Hunter" will be on that list after I get mine in!
I have them all except for the arowana, I just don't have a tank large enough to house one for life.

This is assuming you can actually keep it in an aquarium. Not that you can't keep an ATF in an aquarium, but most people will never be able to afford the addition onto the house to house such a fish.

So my list on has home hobbyists capeable fish.

The most aggressive IMO:
DOVI



Most dangerous:
Mbu Puffer

That is a seriously sick looking puffer. Gonna have to look that one up since you tagged it most dangerous. I already have a couple dovii.

I like Bichirs, but as far as aggression I like Buttikoferi