Well, I would still have to go with the knife. Under most circumstances I'd find myself in a survival situation for in the Pacific Northwest here, a suitable knife would do more for me in a shorter period of time than anything else would.

Now if you were to qualify my physical condition by introducing some broken bones, hypothermia, or maybe even a little shock, well, all I can say is you're gonna have a tough time lighting a bic with all your fingers broken too, or if they are wet and cold, besides which if you are in a soaking rain, firemaking doesn't get a whole lot easier just because you have a lighter. Without an adequate fuel source to feed into a decent flame, it is just a waste of time.

Watch the movie "The Edge" if you want to see how easy it is to go through a box of matches without getting a fire lit. The movie may not have been realistic, but the situation certainly was.

Like I said a couple weeks ago in a similar thread, a good knife and some decent skills should be all you need for all but the absolute worst conditions. Then I think I'd want a lot more than a lighter with me anyways.