I realized after I did the poll that I missed piranhas. I probably could have included Odoe Pikes and the "Gar" characins as well.
x3 for Odoe Pikes being underrated. Odoe pikes snatch up feeder fish so fast that the other fish in the tank don't even know what happened.
I personally like vampire tetras. Most of the time, they are just for looks but that second that they catch food, they are one of the most graceful fish and you can actually witness them precisely catching prey in a way where their front fangs puncture the fishes' swimbladder allowing them to reposition it so they can easily swallow it whole.