I like to have BOTH the illumination power of a 6P (or G2 etc...) along with spare batteries + another lower power/longer life LED light ....
I also have an equivalent of Twin task Streamlight : you can swith on 3 LEDs or 6 LEDs or 1 Xenon bulb, in the same unit. Different powers, different run times also.

But IMHO 2 different lights (using the same batteries) are much better, if only for redondancy.
As someone pointed out, a LED light won't do miracles if smoke is invited to your party !! <img src="/images/graemlins/grin.gif" alt="" />
Then a Surefire (or other brand) xenon light will pay for its price.

Anyway, even a somewhat powerful LED light (i.e. Nuwai QIII) will only give 1.5h of full output (and then several hours of reduced output).
Spare batteries are a must, anyway you look at it, if you EDC a flashlight.