There are two criterias we normally use :

1.Choose the closest port for main cargo. 

Suppose you have two suppliers, one in Ningbo with 2 CBM, another in Shenzhen with 15 CBM. Then the best way to consolidate the container is to deliver the Ningbo goods to Shenzhen for loading. As moving 2CBM will be much cheaper than 15CBM.

2.Choose the main ports. 

Taking one case in 2022 for FIFA hotel project. Factory located in Jiangmen,  total 250containers furniture. But we finally shipped all these container from Shenzhen port even there have barge service from Jiangmen port directly.

Why we take Shenzhen ? Cause main ports means more carriers with different shipping routes and cost options, also mother vessel load directly. If we go Jiangmen port, first no much more carriers option, and barge vessel space no enough for big quantity order. In short, more choice for you at main ports.