Halogens or LED beightness.... it all boils down to lumens and candlepower and the ability to see the road.

I'll add that there new Luxeons LEDS that are 5W, with an output of 120 lumens. a 10-watt halogen bulb will put out about 140 lumens..
Considering that the runtime of halogens vs. the 5W luxeon. you get much more run-time over weight ratio for batteries. the 5W Luxeon consumes about the same energy as a 1-3W bulb. suitable for AA batteries..
Albiet, there aren't any affordable 5W LED systems yet (each LED costs ~$30), but there are makers that build systems containing 3, 3W systems that have (50 lumens * 3 = 150 lumens ).