If I could only use ONE flashlight, I'd start with my Gladius. This assumes that I have my belt on.
If I'm not wearing my belt, I'm probably in bed, so I'd just reach up and grab a light. With that light, I could find a better one. Any LED-modded Mag would do fine, as would a ProPoly or Dorcy 3W lantern. Then again, if I'm in bed, I'm probably asleep with the lights off, so I wouldn't know about any power outage.
Oh, and headlights for an extended outage. Without overhead mains lights, how else could my dad read The Economist on his exercise bike?