I'm sure some guy somewhere dropped $3000 into a bombproof custom light. But for something you can buy now, I'd say the Malkoff MD2 is up there. Surefire is know for durability, but technically all 2xCR123 format unless you have it bored to fit an 18650. Same with Elzetta.
regarding durability and just to forgo the cr123,s!i bored all three of my surefire 6p's as to run on 18650's,this way i feel you get a bombproof of a flashlight for about $30.and a little labor!i found out how to do this on this forum..:wave: