What is the most dangerous ship-to-ship weapon?

Which Glorious Heritage weapon is most dangerous in ship-to-ship combat?

The anti-proton cannon, because antimatter is terrifying at ship scale while nova bombs are primarily weapons against stars.

Nova bombs attack stars and have strategic effects at system scale. That makes them poorly suited to hitting a maneuvering warship. The anti-proton cannon is designed for direct combat and uses antimatter against ship-scale targets. It is therefore the more immediate threat in a ship-to-ship engagement.