I picked Sonny as well because that's the role that turned me into a hard-core Heathen, he just blew me away!
My next choice would be Jacob Grimm. I loved his bumbling absent-minded professor characterisation, I just wanted to hug him he was so adorable! Another good role not listed is Jimmy , the ex-street kid, from Two Hands. I just enjoyed his manic energy in that movie.
My least favourite would be his role in The Patriot. I thought it was his weakest performance, but I feel quite comfortable blaming Mel for intimidating him.