Punk's reign was basically just a mid-card reign for most of it, which is obviously out of his control but it still hurt the image of the title at times. Of course, due to the fact that Punk was around every week, it gave them the opportunity to do more with him on a weekly basis, but it also lead them into fillers like Punk vs Ryback or the whole AJ/Bryan/Kane storyline for example.
Lesnar's reign on the other hand was the complete opposite. They didn't even have the opportunity to book themselves into fillers because they had months to pick out his next opponents and I must say, most of the matches he was in during his title reign were pretty decent. He started it off hot against Goldberg, then had a great brawl with Joe, moved on to an insane Fatal 4 Way at Summerslam and later on had a great encounter with AJ Styles at Survivor Series. The only negatives are the stuff with Braun (/Kane) and the fact that he went over Reigns at Mania/GRR. My point though is, it might just be a part-time-reign but whenever he did show up for work, he mostly put in the work.
But yea, if we're comparing them by entertainment value, it's Punk's without a doubt. Matches were always good and there was always so much going on with him that it legit felt like an eternity when he finally lost the title whereas Lesnar's reign still doesn't feel like a year long reign to me