Sharkfang, more damage, more enemy damage within the radius of the swing, rank 2 weapon skill, plus critical damage and health boost. My opinion, use Sharkfang while looting. Use Treachery's End in voodoo pvp or mollusk battle. But it's your call not mine.
I have to go Sharkfang, although I like both. The freeze and endurance boosts make the difference for me. I rarely need the voodoo assist of Treachery and although the dark curse does help it can not overcome the freeze on Sharkfang. I am happy to have each though, both are fun.