I don't think I can do this. Both of them are great at certain things but not necessarily better than the other.
Punk was the trendsetter for the current crop of talent we see today and he was a better promo guy. Like, with him, he had talking down to a science. I went back to a promo he did against Randy in 2008 and I was like, "Damn. Even back then, he had a strong handle on his words." Punk was also the better heel too. He made you want to hate him no matter what, to the point where he could turn crowds against him. His promo in Tampa in 2013 was the epitome of "fukk you" through the microphone.
Bryan was the more interesting face though and more sympathetic. Punk was the cool guy with an ability to get you behind him because of what he said. Bryan was the more likable good guy because of how he carried himself. He made you believe in him as an underdog and that he was being held down. You could feel that and touch it through the screen. Him winning at WrestleMania was an instant classic moment.
But I can't say one is definitely better than the other.