Alkaline AA vs. Lithium CR123 batteries:

For daily use Alkaline AA batteries are cheaper than Lithium CR123 and most people will be better off with AA if their Every-Day-Carry light is also their emergency light.

But I do not agree that “standard batteries” are an advantage for long term survival applications. If you can stop by the store and pick up more batteries you're not in a survival situation. Alkaline AAs are a compromise to save money, not a functional improvement.

If a separate emergency kit with a light is maintained then Lithium CR123 is a better choice. Lights using CR123 can be smaller and lighter than AA lights. But the big factor is performance: a CR123 light will still have 80% of capacity after 10 years, and a CR123 self-discharges far slower than Alkaline AA batteries in heat and retains much higher capacity in cold environments. A CR123 light will also generally be brighter than an Alkaline AA since a CR123 supplies twice the voltage and much more power than an Alkaline AA.

I recommend that any dedicated emergency flashlight use CR123 batteries in order to be sure it will work (and will not have leaked!) when needed, even if your kit is years overdue for inspection & replenishment, even if your kit is stored in an extremely hostile thermal environment such as a car.

Fenix vs. Surefire:

Fenix has a better brightness per dollar cost ratio than Surefire and Fenix does make some AA lights. But I don't think there's any real debate after handling both that Surefire is more rugged and dependable in harsh environments and under rough handling (I have and use several examples of both brands).

My philosophy is that emergency gear must take care of itself. Normally when I drop a light outdoors I pick it right up and wipe off any moisture. But if a light falls out of my pocket into a puddle during an emergency it may have to stay there a long time while I deal with other more-pressing problems ... and it had better work when I do get back to it. I'm not going to be able to spend the time and attention coddling gear that I might normally do at home even though it's much more important that nothing fails in an emergency.

Fenix makes more sense for most people to use as a daily light. But for a dedicated emergency light that might face rough/poor handling I believe Surefire is a better choice when the budget allows. And for institutions with a “Buy American” preference Fenix is Chinese and Surefire is American.

Other:

The Streamlight 4AA has MSHA approval for use in gassy (methane only) mine environments. Their “Survivor” will likely too at some point given the obvious design goals but it isn't listed yet. Pelican may also have MSHA-approved lights.

The Surefire M6 is the most powerful handheld light I know of short of a HID and is top quality. I was testing one last night against some cutting-edge Q5 Cree lights and none were close to touching it. That may change next year once the S-bin Cree LED ships: LEDs will then have the throw of an M6 and a 3-LED light will have the overall power. But right now the M6 is the king (and costs a king's ransom!).