Adele and Gaga may have to share the throne. Rolling in the Deep is a phenomenon, which none of Gaga's recent singles really being (except Born This Way). But Gaga doesn't even need a hit single to stay more relevant than chart toppers. Nonetheless, they are both pretty big. Justin Bieber falls slightly below, only slightly. He, much like Gaga, is just a sensation through his existence alone. The success to back it up too.
Then I suppose Rihanna would come next, she is pretty popular now in music and social success.
. She could be if she wanted.