Neville, you have a point as I don’t really know how the MO Litvishe girls dress so I shouldn’t have made a blanket statement that seems to include them.
But in regards to chassidishe girls from chareidi families, there is no question that Lubavich girls dress with the least tznius.
And to clarify, there are two areas of tznius: one is clothing that covers all areas that need to be closed, and the other is clothing that does not attract overdue attention even when covering those areas. The fact is that unfortunately lubavich is the worst in both those areas.
Of course there are some very tzniusdik lubavich women, but overall the level of tznius in Crown Heights and in other lubavich enclaves is very depressing.