A lot depends on your power (wattage) output on your bike. Like on my EXC400, which only puts out about 40 watts, the stock set-up works about the best. The Acerbis Dual lights work really good if you've got the ignition to run them(combined-70 watts). Plus, if your ignition is really good you can install higher wattage bulbs then that and they really put out some light!
I had a YZ with the Baja Designs 140 watt ignition and I'd run two 50 watt bulbs. By not going to the limit of your ignition range your lights will tend to stay brighter at lower rpm's.
Glass lenses and halogen bulbs(like the Acerbis HP) are usually the brightest, but you have to put some kind of cover over that glass to keep it from getting cracked by roost, etc.
I have the DHH on my Husky. I feel it has poor light output for the wattage drawn. I have a 130W stator so I have the power to run it. The Baja Designs headlight (street legal version) puts out more light than mine, it uses a H4 bulb 55/60W or wattage of your choice.
I am running an 80W PIAA in one side of my Acerbis DHH and the stock 35W in the other, both on at the same time. The combo is still not as good as the Baja unit at 55W. This is due partially to the beam pattern and partially to the reflector size (larger is better).