Most flashaholics want the most bright in the smallest light.
Li-ion batteries give you the power needed for high power leds in a small package. There are drawbacks with this though...
You don't get anywhere near the runtime from li-ion as opposed to lithium primaries (about half) in the CR123 range, but the voltage is higher and a lot of lights will respond to that higher voltage with more output.
An 18650 li-ion comes off the charger at around 4.2v and have capacities of around 2200 to 3000mah. A ni-mh D cell will only give you 1.4v fresh off the charger but up to 12000mah. So if you put enough D's together to get the required voltage to run your led and associated electronics, you have much, much longer runtimes, with the drawback being the size.
One advantage of C-D lights (mags) is you can get bigger heatsinks into them and in turn drive the LED a lot harder to get the maximum output from it.
If you're after some decent C and D lights, mag mods are the way to go. You have a wide variety of emitter and power options that means you can basically build the light YOU want and not have to settle for what the manufacturers are selling (yes I do want a single mode 4D pumping 1000+ lumens).
For an inexpensive but bright light, get yourself a 3-4 C or D mag, get one of
these and some batteries of your choice. It's not the greatest drop-in but it is bright and will give you 400+ lumens from alkalines for quite a few hours. Will cost you about $50 all up and there's no other light that will give that kind of performance for less and be brand new.
Wayne from
Elektrolumens will build a 3D SSC P7 for about $150 and his work is awesome. Or for $299 you can get a Blaster NG
.
Chris of
Mac's Customs is working on an MC-E drop-in for a mag that will be just awesome once it's made.