I'd take my poor katana skills over my reasonable knife skills, if I'm facing a long weapon.Aikido includes some basic sword forms, so if I had to choose a traditional weapon, I'd go with a katana for the same reasons. But, my switchblade comes to mind as it's the only bladed implement I carry and use every day, know the balance of, etc. Plus, it doesn't limit my empty hand techniques.
Edit: Does it count if I mount a bayonet on a loaded M4?