Personally I would recommend both for a couple reasons. First, a light on the helmet will attract attention from others on the road as it will move around with your head. Second, if as you are riding you need to direct your attention to something of concern outside the beam of a handlebar light, you can by pointing your head in the direction. But if you are set on not having a light on the bike, certainly a helmet light is better than no light and will have real benefit. As for brightness, it depends on the kind of riding you do and where. Riding on well lit streets will require less brightness than riding a dark trail.