Hmm...well, if that's the case, you'll want something you can pull out and use quickly, I guess - since it sounds like it'd be a weapon of last resort. I'd say that the butterfly knife or switchblade would be good for surprising an opponent, but a majority of those focus more on stabbing than slashing...and slashing would probably be best for you, if you wanted to force distance between you and your opponent. By the time you're in range to stab someone, they're likely to be attacking you as well, because you can't stab someone with much force at the full length of your arm...not to mention that you have to extract the blade if you land a hit, and unless your stab is instantly fatal they could still hit you in return. But a slashing weapon can threaten as far as you can reach, and wounds in passing, which means anyone who doesn't want to take a hit from it would have to be at least out of arm's reach. So I think that might be the better option in your situation.

[Komaeda is thinking this through very carefully, and very morbidly.]

Really, though, this is just from a layman's understanding...theory might be very different from practice.