Re: If you could only own 1 flashlight for the rest of your life.....
Bored 6P with a very durable 3 mode XML. The 3 mode Manafont/Ultrafire XML module is perfect but I've only had it for a year so I have no idea how durable it will be over time. To me, this module has the perfect mix of spot and spill, modes are well spaced and it's a real barn burner on high.
They're quite durable. I've dropped my L2 lego from the top of a CRJ700 (about 12') onto hard concrete, and it didn't fail. Left quite a dent in the bezel of the Z44, but other than that, it's fine. No broken glass, nothin. McClicky is acting a bit funny now, though (sometimes when setting the mode, it changes to the next mode). If/when the McClicky dies, I'll get it replaced (this will be the second one I'll have killed. I don't think anyone else has killed 2 McClicky's yet).
If you could pot them, I can bet they'll be nigh indestructible.
I myself would carry a SureFire U2 (post 2008) with an XM-L in it. Most versatile light I've ever owned (rotary hall effect switch is the best idea I've run across. Lets you change from high to low as fast as you want).
The runtime is also amazing. 12 hours on level 5 (2nd highest level. Only 1 1/2 regulated hours on Level 6, so I avoid that level, except for short bursts when I need the extra bit of light), and estimated 580 hours on Level 1 (estimated 1 lumen). Switching to an XM-L would probably double or triple the output over the SSC P4.
The only thing I could ask of them is to have the modes marked, so you can switch to the mode you want when it's off.
I'd also pot the electronics on the U2, to guarantee that no drop would ever kill it. Better safe than sorry!
~Brian