In order to make it clear which goods are the best for each East Asia Country, I will list it here which are as far known by me. These are goods that brings (almost) the best results (1:1 with NPC) at a normal state of the port.
South China:
Marble
Saltpetre
Western Books
Musk (Super-effective but expensive to get)
Yangzhou Chestnut (Indirect-method, super-effective)
Inca Rose (Expensive to get, unless doing Lima Dungeon)
Jade (You can get lots of them from Pegu (with jeweller trade) or Palenque Dungeon)
Tourmaline
Korea:
Glasswork
Tobacco (Not good at Pohang due high backstock on Luxery)
Inca Rose (Expensive to get, unless doing Lima Dungeon)
Ruby
Eye-beads
Tourmaline
Japan:
Glasswork (Not good at Sakai due high backstock on Crafts)
Wine (Nothing to say but… easiest to get for most, but hard to peform nanban with due high backstock of alcohol by players…)
Yangzhou Chestnut (Indirect-methode, super-effective)
Inca Rose (Expensive to get, unless doing Lima Dungeon)
Eye-beads (Not good at sakai due high backstock on Crafts)
Tourmaline
Taiwan:
Saltpetre
Western Books
Musk (Super-effective, but expensive to get)
Glasswork
Yangzhou Chestnut (Indirect-method, super-effective)
Inca Rose (Expensive to get, unless doing Lima Dungeon)
Uncharted Waters Online (El Navegante) 