Single light on bars. Helmet light is useless in fog, snow, mist and rain...the droplets reflect the light and it becomes a blind!
Bar mount all the way. I was running around with a homemade job until 2 years ago when I landed a l&m Seca Race. Very bright but uses an intelligent beam pattern so lights up front of wheel as well as projecting down the trail. Really is no need for a helmet light when the light pattern is so usable.
Of course it is all personal choice but the bar-only is the only workable solution in my book.
Saying that I have tried several helmet-mount lights...they do work but the drawbacks outweigh the positives for me...I don't jump so don't have any issues with that. Helmet lights last year were making me think otherwise until I went back to the Seca...the beam pattern instantly removed the need for the helmet light...