The way the discussion went, if you asked a person from North Sudan what is considered the National dress in Sudan, (s)he will automatically say "Jallabiya" and "Hima" for men and "Tob" for women! But I find the argument not quiet right. I feel Sudan doesn't have one!
A national dress should be representative of the whole country. If you go to the village in the southern most corner of the country or anyway where else people wear it. People are identified with it et cetra. Does it happen in Sudan?
The people in Northern Sudan (who happened to be the majority) wear the jallabiya and tob. It has become the norm and been taken as the national dress. It is more the traditional dress, than national. However, some people in the south don't like it. That said, the Dinka and some of the tribes have a much shorter form of the jallabiya, usually made from colourful materials and end just below the knee. It is convenient for going with it to town, if you know that most go naked when living in the cattle camps.
What is commonly worn down south are the traditional skirt with loose cloth wrapped round the body and tied over the shoulder (called the laou?). It is common among the Shilluk and the Bari tribes in the South. The men go around in shorts!
Sorry, couldn't get nice photoes to illustrate my post.