There's a whole forum (candlepower) dedicated to this. People there are as avid, expert and enthusiastic as any audiophile you'll meet. To me there are three possible types for your use: a small handheld unit, a small right angle hand held unit, a headlamp. I've been building my emergency store/flashlight collection and am committed to both the CR123 and AA battery units. A 1-battery light is small with great output. I am partial to Sunwayman LEDs - they have a really nice right angle, all metal unit for about $60. Another very good brand is Fenix and they make an adjustable right angle light. The good thing about such lights is that they can be set on the ground and still provide light or you can clip them on your waist or shirt pocket and they provide light. A good headlamp for cheap is Coast Led Lenser H7 (~30 street); it has both an adjustable beam (flood to spot) and adjustable brightness. Plus you can adjust the tilt. I have one and with these features, it's easy to set it up to read.
If you get a multispectrum light with UV output, it can double as an ID and bill check for counterfeits. Best place to buy batteries is Battery Junction; by far the cheapest price on CR123 batteries. I bought 100 Rayovac (made by Panasonic here in the US for them) for 115 bucks; compare that to 5 or 7 dollars per battery at my Rite Aid or Ace Hardware. They carry every imaginable battery and most every brand of flashlight. And if you do happen to browse candlepower forum, you'll find that people collect flashlights like we collect cables and amps. As for brand of LED, Cree R5 and XML are their newer LEDS; XPG is okay, too.
At the highend for EDC (every day carry) are Malkoff Devices and HDS. I find that I prefer a click on device (usually on the tailcap) rather than a twist as it only requires one hand. If I were specifying a non right angle light: 1 CR123, click on with at most three settings, can stand on it's tail, has a groove bulit in to allow a lanyard. If you must have the best, SureFire makes excellent lights - I am waiting for my headlamp to come in. Another one would be Inforce MilSpec. These lights can run up to $400 but they will last forever and probably are the toughest things out there.
Also, the way the highline LED flashlights are designed, extra battery capacity does not increase max light output, only runtime. A 1-battery unit is good in that in an emergency, if you only have one battery, it will work and if you have multiple such lights, your battery supply can be spread out to others in need (family, friends etc).
