for light output, a gage of comparing is lumen output. More lumens = more light. It might also be measured in candlepower. I don't know any comparisons to judge by right off hand, but the higher the number, the brighter the light.
the WalMart I work at has a Coleman battery-powered LED flashlight range there, plain white and also white/red/blue LED. I've seen some bright LED flashlights before (A friend of mine was building a "lightsaber" using a polycarb tube and an LED, it was very, very intense), and LED's are way more battery-friendly than bulbs.
Unless it's something for a long-term survival situation, ie bomb shelter that likely will sit still for many years, I'd just go with a battery-powered unit and keep spares for the rare just-in-case situation.