Haha, I posted the same
thread over in the Electronics/Batteries section yesterday and got very similar answers, and maybe even the same one from TMG. LOL.
What I decided was, if you want maximum brightness, then go with primary CR123s or an IMR 18650.
If you want similar brightness, but maybe not quite as high when measured, and more runtime, then go with the AW protected 18650 (LiCo) with 2600 mAh capacity. My main determinant was
this battery test done by old4570.
Unfortunately for me, the sole 18650 I have is the Eagletac, which fairs the worst at delivering the power this thing needs. I think I will order an AW IMR.