All the 6-V 2,4 W headlights will work, whether they are LED or halogen. That being said, you have two or three practical possibilities:
1. Lumotec IQ Fly
It uses LEDs and is designed to throw the light on the road. It is about 4 times brighter than the round (standard) Lumotec and about 3 times brighter than the famous Schmidt E-6. The beam is designed to throw most light on the road with a wee bit spill light on the sides but not all around. Not only is it very visible to others, it also does a very nice job to lit your way, even on wet asphalt. Unless you do lots of riding on totally dark roads, you won't need more. And at 90-100 $, the price is interesting.
My only (minor) beef: there is some spill light towards the top and I don't like that. A bit of electrical tape on the upper part of the window solved the problem.
2-3. Schmidt E-delux and Supernova E-3
Both these lights are twice more expensive and both produce almost twice the light.