I've voted the Deathstar II but I prefer the SSD Eclipse, that is hell of a ship, the super laser of the deathstar with the cool looking of a star destroyer
I'd say either the World Devastators or the Star Forge. They were both leagues more efficient than the others. I think destroying an entire planet is just silly. I'd say probably the World Devastators win for me because they could self replicate eventually, and you could be more selective with what they well, devastated.
The Star Forge wins for me, because of it's unique nature as a factory rather than a "true" weapon. It is the only one that can help whoever controls it actually maintain control the galaxy instead of using the Tarkin "rule through fear" doctrine. In combat, the disruptor field would have been quite effective at keeping enemy ships far away from the Star Forge itself. Not to mention, the true extent of its power to was never known, even to its creators. Darth Malak's "experiment" was probably only the tip of the iceberg.
World Devastator, definitely. You can suck up enemy bases, fleets, and even planets, and build your own fleets and armies out of them! Now that's what I call irony...
well, in function, it is a dark side relic which feeds from Rakata's star and the dark side to create years of buildig in mere minutes. it is also in possession of a disruptor field, destroying ships which get near the station. so, all in all, it is both a weapon and a tool.
well it's ability to feed off the dark side and throw endless amounts of well anything makes it a force to be reckoned with. a superweapon doesnt have to have a giant laser on it to be a superweapon.
not to mention argue with wookiepedia. it lists it as a superweapon