Clarkson has sold 10.6 million albums, 15.9 million tracks and has had 4.2 million radio plays, according to Billboard.com, ranking her the top graduate from "Idol." Underwood has 11.5 million and 13.9 million for album and single sales, respectively. The country singer's also had 2.4 million radio plays since she won "Idol" in 2005.
The third most successful "Idol" never won the crown and wasn't even a runner up: It's Chris Daughtry, who fronts his own band, Daughtry; they have sold 5.7 million albums.
