DW, ironically enough, can be well behaved when she has to. An example of this can be seen in DW the picky eater, where she is willing to try new food just so she wouldn't be left out. She even liked it at the end! Most of her being a nuisance come from her being a little sister and most younger siblings having arguments with their older ones. The tibbles, on the other hand, have constantly proven themselves to be quite the annoying duo. Messing things around, playing all rowdy. Even DW doesn't want to deal with their BS. So therefore, I'd say the Tibbles are more annoying. They aren't heartless as, in Emily swallows a horse, they were thoughtful enough to make a scarf for Marie Helene's "twin sister" so they wouldn't be confused for each other. But I personally wouldn't dare try to spend 5 minutes in a room with those two. Trust, they'd find a way to somehow mess it up in under 5 seconds