My head light choice would be one of the current generation of LED's they power up quickly and provide a goodly amount of light, they are also not prone to bulb failure. I have been using the
B&M IQ Lumotec Fly Senso Plus on my larger bike and have been very pleased with it. I am going to give the
Spaningia Luceo LED a try on my R20 folder build up. That bike has an Sturmey Archer AG hub on it, talk about heavy and notchy!
Aaron