Forget your numbers, this is about making a noticeable mark, not just some deluded stan (non)iconic moment, on pop culture that will stand the test of time. Think Madonna's Sex book, BAT look, etc.
Miley has this:
Thanks to Disney she's etched into the childhood of most kids in the Western world.
She's continued her presence in their lives as she and they have grown up with a video that spawned a viral internet meme, catch phrase and numerous parodies and commentary.
This was the hot topic for weeks - columnists, to TV talking heads, to academics had their say.
The tongue has never before been such a prominent feature of a celebrity.
Both have left a TREMENDOUS impact. Back in 09/10 you couldn't get bigger than Gaga, her fashion was ALWAYS a hot topic, her performances even her sexuality and the whole Madonna mess lol. Gaga in a way made pop culture an EVENT again. I remember people just perched for Gagas next outfit or video.
Mikey has sustained amazing longevity. Hannah Montana is probably the most prominent DC show of our gen. The music also sold much better than others in its lane. She's grown up in the publics eye and had to prove her independence. Her VMA performance last year has already gone down in history. It's an iconic representation of society's expectation of its child stars and their personal freedom/independence.
In conclusion, the question is sort of unanswerable lol
Miley tbh. She was on the second-biggest Disney Channel series ever and that show alone influenced everything that channel would ever air in the future. Plus, Gaga never really defined a year like Miley defined 2013 IMO.