But if I had to choose an actual "weapon", I'd choose Excalibur, mainly because it can take down most of the other superweapons. The Ark Bird, the SOLG, OLDS, the Gleipnir, you name it. And supremacy is the strongest weapon. Megalith, Stonehenge, and the Chandelier are the main contenders, which I suppose Excalibur could take down based on the fact that it probably uses reflective mirrors to take down long range targets from above.
If I remember correctly, even Megalith has a limited range, as well as the Chandelier and Stonehenge.
But again, I would say the greatest weapon are the Aces that can have a total of about 100 standard missiles on one aircraft and high missile speeds.