I think it goes more to whoever has the more trying set of circumstances. Most often, that means whoever is going uphill because overall, it's harder work (not that downhill doesn't have its challenges). Most of the time, its been my experience that the uphill climber has the right-of-way. But I do think you need to evaluate each situation and determine who would benefit the most from not having to stop. When you're lugging a pack uphill, you usually want to keep moving, whereas when you're letting gravity push you downhill, you can stop and easily get moving again by simply "taking off the brake" and letting gravity continue to do its thing.
CaT
