I started with season 6 on FOX! I will include all 15 though...
Season 1: Kelly Clarkson & Justin Guarini
Season 2: Ruben Studdard
Season 3: Fantasia
Season 4: Umm. Maybe Carrie. Don't really have a fave from this season...
Season 5: Chris Daughtry
Season 6: Melinda Doolittle
Season 7: Carly Smithson, Michael Johns, David Cook, and David Archuleta!
Season 8: Kris Allen, Allison Iraheta
Season 9: Siobhan Magnus
Season 10: HALEY REINHART.
Season 11: Hollie Cavanaugh
Season 12: Amber Holcomb
Season 13: Caleb Johnson
Season 14: Joey Cook, Clark Beckham
Season 15: Avalon Young, Dalton Rapattoni, Trent Harmon.