Hmmm. Well for me, like most of you, my choices are pretty endless. If I have pants on, then I have a solid locking folder and a MT on me.... but for the sake of trying to limit what I can take to one fixed blade.... it is nearly impossible to think of a scenario where I can get to one fixed blade, and not one of several.
But playing favorites, I would want my Gossman Kephart or Mini Tusker, any one of my RC/ESEE blades (yes I trust my life to all of them) or my Ontario TAK (mostly because it is the one blade I have used and abused more then any other).
I am pretty much against the idea of anything too large, simply because it is hard to conceal and I do not want to stand out for any reason. Just an opinion, but carrying a SP-8 or my Machete is going to make me stand out a lot more then a concealed Izula or Gossman PSK. Honestly, I never carry blades that big now, and I am kinda of of the mind set of taking what I know and what works.