That depends how you define great.
Great as in powerful and almighty, you can't really argue with the tank when you got bad boys like the Arbrams :tank: . But then again I guess the greatest weapon of all would be the nuclear bomb, giving man the capacity to end the world as we know it within hours.
If you mean great as in serving a moral and virtuous purpose, the helicopter for quick extractions of the wounded within the golden hour takes the cake.
If you mean great as in all totally sick and cool, this ones really up in the air. So many things, I can't choose one. Flamethrower, .50 cal, fighter jet, aircraft carrier, nuclear submarine, I could go on forever.
:rambo: