Queen of the Decade doesn't just mean "sales", it's a combination of many things. The only people who should be considered of the 4 are Gaga and Rihanna.

Rihanna and Gaga are definitely the biggest stars. Adele has some insane stats. You could make a case for any of those.

adele had huge success with 21 but its kinda like calling norah jones the queen of her decade.she sold hella records too but she wasent the queen of the decade..britney was so no

katy is cute...and thats all. shes no queen. she hasnet even reached that level of interest with people

gaga is definetly an icon of this generation....and thouh i think rihanna (an icon for ths generation as well) is a bit more relavent to the public right now (check oprah ratings) , usually there are two girls who slay every generation , and the black girls usually fall in second place.
madoona and janet. britney and beyonce , and now rihanna and gaga....i think its really a toss up for who will be remembered as the queen. their both superrrrrrr famous and succesful, and have their strong points.....gaga has touring and album sales... rihanna has overall interest/popularity (ex:internet stuff and just always being a hot topic) and single sales.....but they both have each other's strong points but not as much as the other, but enough to be considered for queenship.......and they are leages ahead of adele( even wit her sales) and katy #truth

Adele.

This is so sad

And right now, obviosuly Adele. And I mean if she keeps it up, she WILL be the queen of the decade.

In overall influence an an artist? GAGA.

Musically and sales-wise? Adele, and it's not even close.

Monsters need to learn, it's not "who is your favourite artist" every time. Grow up.