Most definately Dumbledore is the more powerful. It's the same reason, in the end, that Harry will be more powerful than Voldemort. Both Harry and Dumbledore aren't afraid to die. Voldemort fears death more than anything else. Look at the extremes he has gone through to defy death - drinking unicorn blood, splitting his soul into 7 pieces, etc. Harry proved he wasn't afraid to die when he jumped out from behind the tomb to face Voldemort like a man and stand brave as a testament to his parents. Albus proved he wasn't afraid to die when he sacrificed himself for the greater good. Voldemort's fear will be his downfall.