My money is on the Death Star.

A single ship, no matter how advanced the shielding, would unlikely be able to absorb or deflect the amount of energy shot by a cannon that can destroy a planet.

As a SW turbo laser is antimatter encapsulated in a photonic package (more similar to a Trek photon torpedo than a phaser), the amount of antimatter in a Death Star blast, would easily be able to overwhelm a Borg shield.

Additionally the defense of the Death Star are built around a large scale attack. A single Borg cube would be unlikely to be able to withstand the defenses excluding the main cannon.

This are just my thoughts though, anyone care to comment?