I used Sylvania Silverstar 9003 and they are great. I have one on my VTX as well... nice and bright. However, I did get some adapters for the bulbs and bent 2 tabs back on the 9003 bulbs. If you run high beam during daylight, they might not be the bulbs for you... as their life span on high beam is shorter, or at least that is what I have heard or read.
Oh and you probably heard that you should NOT touch the bulb (glass) with bare hands as that will cause the bulb to burn hot or burn out with any oils from your hands left on the glass. I used some Dr's rubber gloves and made sure I wiped the bulbs off before I put it in. The one on my VTX has been working for 3 plus years and Valk going on 2 years.
Here is some other info for ya from Rattlebars.com
http://www.rattlebars.com/valkfaq/#HEADLAMPS