Which set Bonus are more effective? Demonic Bonus with 50 double strike or Haunting Bonus with 100 total damage?
it kind of Depends.
Demonic Bonus requires +50% Movement Speed on your Equipment to get a +50% CHANCE for each of your attacks to hit twice instead of once. this would go well with Momentum Set which give extra damage based on how much extra Movement Speed you have, plus you get to run around faster and can move out of the way of ranged attacks easier.
Haunting Bonus requires +40% Clearcast to get +100% Damage to ALL ATTACKS. whenever Clearcast activates, your attack is cast for free (using either Myth Stone or Legend affix). with at least one Legend Clearcast, with Clearcast +40% or higher activated, any Spells with Cool Down have their CD reduced to 0.5 seconds. Spells with faster CD’s than 0.5 seconds will have their DPS go down (haven’t tested this, but it sounds logical).
it looks like Haunting Bonus is better for most Builds because it takes up less space to work, I think. also, it makes using Barbarian (lowers your Mana) & Push the Limit (increases the cost of your Spells) Affixes easier. but it is possible to make Demonic Bonus just as good, but it would take up more space, especially if you got your Double Strike up to +100%.
even if you don’t have enough Resource to cast a spell, if Clearcast is activated while trying to cast a Spell, the Spell will be cast without using a Resource. I had fun testing this with +75% Clearcast (I needed Epiphany (5) to do this).