Noumea, New Caledonia has very easy check in - they come to your boat. To check out you need to walk a ways and visit 3 locations, but it goes easy.
Vanuatu depends on where you arrive. At Tanna (and you need to go there to see the volcano at least) you need to take a 2 hour four wheel
drive trip across the island. On Aneityum, if it's during cruise ship
season then it's really easy. The main city, Port Vila is worth a visit and check in and out goes pretty easy. So, I wouldn't us that as your reason tochoose one over the other.