I used a H4 Sylvannia Silverstar. Got it at the autoparts store for about 10 bucks. As far as "brightness" goes, they techincally are not brighter. They are the same wattage as the stockers. However, when it comes to "whiteness", there is a huge difference. The light is much whiter. I like them and have them in 3 vehicles.
Until I decide to go HID...I put in one of the Sylvania Silverstar Ultra bulbs...the 9003 (H4) fits my bike....huge difference in the light, especially on high beam out in the boonies. WELL worth the $25 price.
none of the auto store carry a H4 bulb around here, mine went out last month, ended up at the local MC shop, non Harley, but they had one for GW with same No works fine.. 5 bucks less and 60miles closer the my dealer..
+ one for the Sylvania Silverstar I have the Motorcycle Metal HID for my headlamp must say it rocks and I use the Sylvania 880ST in the aux lights they are supper bright and got them at Walmart for 14.00 each.
The silver stars are brighter or whiter, however you wish to explain it. My personal experience has been that the super white ones tend to burn out rather quickly. I have used the 9003 and the st4 version with the same results. Last time I got a regular silver star (not the white one) and it seems to be lasting well. Only time will tell. I would like to do HID as well, but am a bit uncertain about legality issues as the only "legal" one I can find is $500. It's not that dark at night in the city.