It really depends. I mean One Piece and Naruto aren't toned, but pull it off really well. When you see something like Air Gear then it's like hmm this is really something different. something like that would not look as good not toned. it really depends on the style of drawing and all i think
I would have to say toned i guess. if done correctly it really makes the image look a whole lot better, but the bad thing about tones is that if over used or done wrong it can really destroy a piece. just a personal opinion.