Mine's Nobody's Home. I just recently discovered Avril Lavigne a few months ago, although I had heard Complicated and some other songs of hers before. Just bought tickets for her tour! She seems so awesome.
Edit: Take Me Away and Slipped Away are also some favorites of mine :) I guess I just love the whole album! But I still haven't heard her whole discography yet. I'm an artist myself and I just admire her vocal abilities. She's super talented.