Armchair swcnts are ballistic conductors. It matters quite a lot how that carbon is oriented.
How well do they conduct? At the moment aluminium is kind of the "sweet spot" between weight, cost, and conductivity.
Ballistic conduction means 'perfect' conduction in a sense. There's no resistance. It's only for armchair swcnts though. Other metallic swcnts are also great conductors, but if you separate out the chiralities (semiconductors, etc) you might as well separate to just armchairs.