There was a time where my answer to this would be Fist of the North Star. I grew up watching that show on Starz ever Friday night/Saturday morning (along with Dirty Pair/Flash. Best night ever for a young lad), and while it still is a show I love to death, I don't know if I can call it my favorite. I really love Gunslinger Girl. Like, ridiculously so. But I never considered it to be my all time favorite. There's also Infinite Ryvius.....I'm just gonna say Gunslinger Girl. It was the characters what got me.