As for the most no.1's this era, Queen Bey is looking to take that title
Best opening numbers, Britney no doubt will open with 500K+
Most top 10's, Rihanna based on the fact she releases 20 singles PER ALBUM
End of the year best selling album + singles combined, best music videos, Gaga is primed and ready
And Katy Perry will take the left overs (no shade intended, but I can't really point out a real strength in her as of now)