Now, I only took a cursory glance through all 4 pages, but it looks like Henry's designs (HDS, RA, NT) seem to be the favorite. And for good reason! Love them. A little large for a single cell light, but built like a nuclear shelter from the Cold War Era.
However, if I can only have one light, I'm going to cheat and say a light I have no experience with....and only about 20 are currently floating around in the world...
Cool Fall Spy007 Tri-V. This is really 3 lights in one. Aspherical XR-E, MCE flood and XP-G reflector. All in a single-cell sized (2 cell) 123 light. It can be programmed to be .01mA! How long would that last on 2 x 123 batteries? Like my girlfriend from Full Metal Jacket said, "long time". Now, it's not bomb-proof like the RA, but how can you beat 3 lights in one, fully programmable to 14watts of power flowing through 6 LED's? (MCE is really just 4 XR-E LED's, an XP-G and another XR-E). Forget about how much it costs, and just think about the sheer utility of the thing. Rediculous, really.