Well, I've been looking around for a new flash light....
I got a
Streamlight Task-Light 2AA model and I'm happy with it. I also have a
Gerber Infinity Ultra. For hiking, I carry either a
Gerber Tracer headlamp or a
Black Diamond Nightray. I include LED micro-lights in all my PSK's.
County Comm sells a couple great versions for $1.00-$1.50 each, so there's no reason not to have them sprinkled through all your gear and kits. I have an
Inova Microlight too-- about $6 at Target, IIRC. There was some talk about the
Atom Cyclops headlamp on an ultralight hiking forum and I picked one up on sale for $5 and that went in my day hiking kit.
What to look for? Size, weight, lamp type, battery type, battery life, beam pattern, light output, waterproofness and durabilty, and cost.
To answer your question, the Streamlight was ~$20 on Ebay, uses two AA cells and puts out a good white beam with a decent beam spread. Size and weight aren't bad, but the handle is just a little bigger than a Maglite AA, so it won't fit some Maglight holsters. It has a pushbutton switch near the head and two lighting levels plus a strobe setting. I carry it everyday in my urban PSK in my day-pack sized backpack. It is not my first choice for hiking.
In the woods I prefer a headlamp. Walking down a trail in the dark is the most demanding task I use a headlamp for and that's why I went to the weight and complexity of the Black Diamond rig. It has 5 output levels plus strobe, so I can adjust it to task and comfort level as well as battery life. Reading or kitchen duties don't require high light output as they are close at hand. The Gerber Tracer is great for that and is compact and light and uses just one AAA battery at a time. The Cyclops has a mean beam pattern and uses two C2016 coin cells, but it would be okay for general use and weighs just an ounce, so it's a quick and dirty step up from a micro led flashlight.
Battery type is something I've tried to integate. I'd love to get all my gear using all AA or AAA batteries. So far I have a little of each. With the micro lights, it works out that you might as well carry another whole light. Trying to open one to replace the battery and dealing with four tiny phillips screws in a survival situation would be a sad comedy. The Inova Microlight excels on battery replacement as it snaps open and there are no small parts that go flying.
The number of batteries and battery life is something to consider in a survival light. The Gerber Tracer uses one AAA battery, where my Black Diamond light uses three. If the Gerber runs out, I can take one battery from my kit to get it going again, so I can carry a couple spares and know when I am running low. With the Black Diamond, I need three spares each time I refill. Having one dud in three leaves me without a light, etc. The BD lamp does have good battery life on the lower settings, so the trade-offs aren't all bad, but I need to carry six spares to get the same level of security as two spares with the Gerber. It's the same kind of deal with the Gerber Infinity (one AA) vs. multiple cell flashlights-- in both cases light output and battery life is less per "round" -- it just depends on the perfomrance you want.
With hand-held flashlights, I like AA batteries. Some use CR123 cells and give great performance, but the CR123's cost a lot more. CR123's do give higher horsepower to weight in the field and shelf life is good. If you are using the light at work and your employer is buying the batteries, CR123 lights work well

.
Beam pattern is the real toughy in choosing a light and you darn near need ot have them side-by-side in a dark room to really tell the difference. Buying them on-line or untried, I guess finding reviews with beam pattern photos is the best bet.
Good luck!