me and some of my frineds were asking this same thing like 2 weeks ago. we all agreed the borg cube would kick the death star's butt. only cause the borg would just assimilate the death star not only that the death star is a little lacking in the defence part. only when fighters are incoming on it will it have a good chance of anything. My vote would go for the borg cube to win.
What about Battlestar Galactica, a Borg cube, the Death Star and "The Big Show" in a four-way cage match?
Borg Queen and Darth Vader would have mad machine sex complete with pounding pistons and everything. This action forms an alliance that wipes out both the Jedi and the Federation. Then Terminator walks in and they have a threesome.
Size isnt everything, the technology behind them is what counts. Remeber Voyager equipped with the futuristic abaldive sheilding? (series finalé) It managed to withstand being attacked by 3 or 4 Borg cubes, simply because of that future technology is possessed!