Machine gun. There's been enough screen villains already that had swords hidden in umbrellas... It's almost to the point that when you see a gentlemanly rogue with an umbrella or cane, you know he's gonna pull out a sword at some point.
Plus, not that I want to take the "it's not realistic" angle, but how efficient is a sword against Batman anyway? Sure, if Ra's Al Ghul is wielding it, but the Penguin...?