If you have two brain cells, which most of the site lacks, it's clearly Abracadabra since Gaga was able to find global success with a NEW song from her catalog. 40+ weeks on the Global 200 (which factors in consumption from all streaming services) and 8 in the Top 10. It was also critically acclaimed, ranked one of the best songs of the year, and won 2x Grammys, things Katy Perry has always struggled with, and given her output this decade, looks like the struggle is going to get prolonged indefinitely. When you look at how their respective careers have shaken post 2013, the answer resoundingly becomes even more clear and unanimous in the real world. But I understand why some wouldn't be able to comprehend that.