In a sense of sheer, raw, power, I maintain that Aang surpasses everyone else. He proved to be a natural at learning all four elements: he had mastered Airbending by age 12. In 109, he surpassed Katara as a Waterbender easily. In 116, Jeong Jeong said that he had never before seen such raw power in a student. After he got his head around Earthbending, he progressed by leaps and bounds. In 306, we saw how Avatar Roku was able to easily surpass his masters. Once Aang finds time to master each element completely, I am confident that he too will surpass all of his masters.
He has more power. It's that simple.