If you build something like Warrior Tabi > Hydra's Lament (or Jotunn or Beatsick, they all have 40 power) > Titan's Bane > Malice/Deathbringer with 2 defensive items, you get 160 power at lvl 20 (no power pot or buffs), giving you ~346 damage per hit on your ult (120+30% doubled by crit). Malice gives you 120 additional damage per hit (75% of phys power), DB gives you extra 138 per hit (40% of 346).

With 1 defensive item and assuming you don't go 2 crit items for some reason, add 40 power from Beatstick or JW, and you get 200 power. Hit from Wind Fire Wheels deals ~416 dmg, Malice adds 150 DoT, Deathbringer adds 166 extra sauce to your crits.

So if my math is correct, numbers favor DB until you're full build with extra power from red pots and buffs. Feel free to correct me if I'm wrong.