Most important factors:
1. Brightness (lumens)
2. Color (white verses yellow/orange, measured in degrees Kelvin)
3. Life (hours)

Usually the brighter, whiter, halogen lights (Silverstar) have the shortest life so it is a trade off.

LEDs are usually the best because they have the longest life (near lifetime), the whitest light, and are brighter. But they can't always be used everywhere. LEDs are brighter because they are much more efficient -- light output (lumens) for power input, and less power gets wasted in heat.

Any lights that consume more watts than the law allows are labeled "for off road use only", but in fifty years of driving my Porsche with 100 watt H4 bulbs, I have never been stopped because my lights are too bright. Besides, I doubt that few people even know how to measure the watts going into a bulb.

If you are respectful of oncoming drivers, you should never have a problem.

Many of the halogen lights that claim to have whiter lights do that by having a blue coating that keeps the red/orange/yellow components in. Any coating that removes part of the light has to put out less light for the watts in.

Also keep in mind that blue lights are illegal except for emergency vehicles. A lot of the kids where I live, like to put blue coated headlight bulbs in because they think they are brighter; they are not. Really hard to tell which is dimmer: the headlight bulb or the kid's brain.