The best port strategies in Cities & Knights revolve around the brick and the wheat port. The main reason for it is that Cities produce two bricks, and two wheats, but only one resource with sheep, wood and ore. It creates more fuel for the brick and wheat ports, and less for the others.
Port strategies have less power than ore-wheat-paper-cloth, but they’re incredibly flexible. This flexibility allows their users to get Aqueduct fast, defend against barbarians reliably and build missing level 1 city calendar upgrades much faster than many other set-ups.