For me it would be between a Ferrocerium rod and a BIC. I like them both equally for different reasons.

With this in mind, I always have a BSA Hotspark ferro-rod on my keychain and a BIC lighter in my jackets/coats. I figure, if I'm going outside I've probably either got my keys on me, my jacket on me, or both.....therefore, I've always got at least one method on me.

(I've also got a magnifying glass in my wallet, so you could count that as a back-up method.)