I'm going for Deathstar. They can use weapons which are based on kenetic enegery. Since Borg can only adapt to frequency weapons Kenetic weapons would seem to be able to decimate them.
(Plus the Borg were killed by Picard with bullets and always die from Knife wounds (from Worf))
(Plus the Borg were killed by Picard with bullets and always die from Knife wounds (from Worf))