If I can get to choose my favorite American Idol contestants back when the show was at its peak, it would be Adam Lambert, David Cook, and Kelly Clarkson.
The only reason why Clarkson is at three is because I knew most of her songs after her stint. For Cook, he did well re-arranging a lot of good songs, with Michael Jackson's Dirty Diana and Billie Jean, and the chick movie soundtrack-ish cover of Mariah Carey's Always Be My Baby, to name the best ones on top of my head, but post-Idol hasn't been as booming as it was with well, most Idols.
Adam Lambert is a different story.
Yes, he reminds me of The Weekend now, but his songs are awesome. I really believe that the Southern votes destroyed the show because Kris Allen over him is just nuts.
Whataya Want From Me is my favorite Adam Lambert song and what's nuts is that he does it better when he does it live.